Domestic Water Treatment for Homeowners
On-Line Version Of American Ground Water Trust's
Consumer Awareness Information Pamphlet #3
The American Ground Water Trust has prepared this consumer information pamphlet to help people make good economic and environmental decisions about water treatment. There are many water supply specialists who provide water supply products and services; this pamphlet will assist you to obtain the professional help you need.
The contents of this pamphlet for consumers will:
Not all ground water requires treatment before consumption, but when it does, the design of a complete, effective, and safe home water system is not for amateurs. The American Ground Water Trust hears all too often about inappropriate, or oversized conditioning systems purchased and installed by do-it-yourself homeowners or sold by door-to-door salespeople who may use scare tactics, or who frequently don't know the first thing about basic water chemistry or microbiology. Correct selection of water conditioning equipment may require an understanding of microbiological and hydrochemical processes. Let the buyer beware!!
The pamphlet starts with some basic information about ground water and wells. Succeeding sections include descriptions of the common causes of poor water quality and frequently used domestic water treatment methods.
With the increasing movement of people into suburban and rural areas, more homes are relying on water wells. Today's drilled wells, built to strict code specifications, produce safe water for millions of Americans. About 110 million people in the US are served by municipal water from wells and another 40 million people use ground water in homes with private wells. Water wells are "engineered holes in the ground" that are constructed to access water that fills the cracks and pores of rocks in the earth's upper crust. This water in geologic formations is called ground water. It soaks through layers of earth and rock from rainfall and snowmelt. Zones of rock saturated with water are called aquifers if they can supply water to wells or springs. Aquifers can occur in solid rocks that may be cracked and fractured and in buried layers of sand and gravel. Some aquifers are huge and extend over hundreds of square miles; others are very localized and may only be adequate for supplying a few hundred gallons a day.
In the United States the quantity of water in underground storage is 20 to 30 times greater than the amount in all the lakes, streams, and rivers combined (including the Great Lakes). However, we cannot take our ground water resources for granted. Once pumped from the ground, it takes longer to replenish a ground water supply source than a surface water source. Recharge is relatively slow because the replacement (recharge) water from rain or snow melt generally must filter down (infiltrate) slowly through the soil and rock to the ground water table. It is also difficult and expensive to cleanup contaminated ground water.
"Pure" water does not exist. All natural water contains some dissolved gases and minerals. Ground water quality is influenced by the chemical make-up of the geologic formations in which it occurs, and the length of time that it has been underground.
Overall, ground water is cleaner and purer than surface water. Most ground water moves very slowly and its long travel time in a dark cool environment means that it has few, if any, of the millions of microorganisms that are virtually always found in lakes or rivers. Ground water is usually free of sediment and constant in temperature. In addition, ground water is naturally protected underground and less likely to become polluted than surface water. However, ground water may be more mineralized than surface water because its slow movement gives time for it to dissolve minerals from the rocks it touches, allowing it to pick up various rock-related chemical constituents.
These constituents may include trace levels of iron, manganese, calcium, magnesium, sodium, bicarbonate, silica, sulfate, chloride, nitrate, and fluoride. Small amounts of these elements and compounds do not usually cause health problems in drinking water. In some cases, however, the levels may be high enough to affect the aesthetics of the water (e.g., staining, hardness) and must be reduced.
Some dissolved constituents can be removed or reduced with treatment equipment. Home water treatment is often a simple cost-effective solution to water quality problems, particularly in rural and suburban areas. Moreover, many persons using municipal water supplies supplement the municipal treatment with home water treatment units. In order to obtain good results most water treatment units require attention and maintenance. An improperly maintained treatment unit may be ineffective and may cause additional water quality problems.
Homeowners with wells have primary responsibility for the quality, and quantity of their water supply. It is recommended that the drinking water supply be checked with an inexpensive laboratory test each year. Water quality problems can usually be remedied with appropriate water treatment equipment. About 30 percent of the homes in the United States have some kind of water conditioning equipment to meet personal or recommended water quality standards.
Three general categories, physical, biological and chemical can describe water quality. The effects on water quality in each category are described below.
Taste, odor, turbidity, and color are the principal physical properties of water that are noticed by the user. Objections are usually made for aesthetic reasons. However, these characteristics may also indicate possible health hazards or the potential for reduced operating efficiency of well equipment; and therefore should not be ignored.
Taste and odor can affect the quality of water by tainting certain foods and vegetables and by reducing the palatability of foods cooked in water. The main sources of odor- and taste-bearing substances are harmless organic materials like iron bacteria, and certain inorganic chemical constituents such as hydrogen suffide.
Hydrogen suffide is the primary cause for the "rotten egg" taste and odor in water. In high concentrations it is a flammable, poisonous gas that is highly soluble in water. It is also toxic if inhaled in large amounts. For these reasons, make sure well pits and well houses are properly ventilated. Hydrogen sulfide may be derived from the action of sulfate-reducing bacteria, or by the decomposition of organic matter, sewage, and certain industrial wastes. In addition to its unpleasant odor, hydrogen sulfide is corrosive and causes black stains on silverware and fixtures.
Acidic (low pH) water can leach copper out of pipes causing a metallic taste, especially when the water is not flushed from the pipes frequently. An odor problem may occur with the presence of iron bacteria, which may cause a musty or swampy smell in the water.
Most taste and odor problems are solved by eliminating the substances that cause the problem. Treatment techniques include activated carbon filtration and/or oxidation using chlorination, potassium permanganate, ozonation or aeration.
Turbidity is a visual haziness in water caused by the presence of insoluble suspended particles. Generally, turbidity is more common in surface water than ground water because ground water moves too slowly to carry particles of sediment. Turbidity is undesirable for health as well as for aesthetic reasons because turbidity can interfere with disinfectants and can "piggy back" microorganisms.
Discolored water may contain substances such as organic compounds derived chiefly from the decay of plant and animal matter. Certain metallic ions, such as iron and manganese, sometimes color water yellow, brown or red after contact with air, heat or after disinfection with bleach. Highly discolored water is objectionable because it may stain household fixtures and clothing as well as reduce the water's visual aesthetic appeal.
Treatments for turbidity and color usually involve settling or filtration.
All natural waters, regardless of source, are likely to contain some microorganisms. Microorganisms are too small to be seen without a microscope, and include viruses, bacteria and protozoa. Some types of bacteria cause disease and some impart taste, odor, or turbidity to water. Most types of bacteria are not pathogenic (disease- causing).
Ground water usually has fewer microorganisms than surface water. Bacteria and viruses (ultra-small microorganisms) either die-out, or are removed from water as it infiltrates down through soil and rock, primarily through filtration and adsorption. The number of bacteria may be reduced through competition for nutrients or predation among themselves. In very fine sediments, mechanical filtration may occur as the space between the soil and rock particles acts as a sieve to screen microorganisms out of the infiltrating water.
Adsorption is the adhesion of a substance to the surface of another material because they have opposite electrical charges (like magnets). Soil particles, bacteria and viruses have very slight electrical surface charges based on chemical composition. As the bacteria and viruses pass through the soil zone, they are attracted to negatively charged soil particles and held in-place.
The ability for soil and sediments to filter and adsorb bacteria and viruses depends on the length of contact time between the water and the soil. Longer contact time increases the effectiveness of the soil at removing the microorganisms. Contact times may be increased by reducing the rate of water flow through the soil layer and/or by reducing the concentration of bacteria or viruses within the infiltrating water that the soil must treat. Maximum effectiveness occurs when there is a slow rate of infiliration and thick (deep) soils.
Domestic waste water, feedlots, surface runoff, and other pollution sources may sometimes contaminate ground water. In these situations, ground water is impacted when the soil zone receives more of the nutrient compounds than it can use (short contact times). The excess may be carried down to the ground water or washed into nearby ponds or streams. Ground water from deep, drilled wells does not need disinfection if tests prove that it is free from microorganisms; however, shallow or dug wells usually require periodic or ongoing disinfection.
Pathogenic (disease-causing) organisms occurring in water range from ultra-small viruses to microscopic bacteria to relatively large protozoa. Bacteriologic and protozoan pathogens are known to cause typhoid, dysentery, cholera, and some types of gastroenteritis. Viruses can cause human maladies including polio, infectious hepatitis, and some forms of gastroenteritis.
Biological contaminants are most effectively eliminated by disinfëcting water through oxidation (e.g., chlorine disinfection or ozonation), filtration, or ultraviolet irradiation. For each method the equipment must be specifically designed for the intended use and properly maintained. Regular bacterial analysis of the treated water is needed to ensure that adequate treatment occurs. Filtration is more effective in controlling bacteriological impacts when used in conjunction with oxidation or irradiation treatment.
A chemical disinfectant should be effective on many types of pathogens regardless of their quantity and it should be able to kill all pathogens within a reasonable contact time. The chemical should also be safe and easy to handle and it should not make the water toxic or unpalatable. In addition, the concentration of disinfectant in the water should be easy to monitor and the disinfection should provide residual protection against possible recontamination.
Disinfectant-dispersing equipment should be automatic, require minimal maintenance, and treat all water entering the home. It should also be fail-safe so that no one can unknowingly use or consume contaminated water.
Additional information on disinfecting wells for bacteria may be found in the American Ground Water Trust Consumer Awareness Information Pamphlet #10, "Bacteria and Water Wells."
Dissolved substances in ground water may include ions of iron, manganese, calcium, magnesium, sodium, bicarbonate, silica, sulfate, chloride, nitrate, and fluoride. Other dissolved mineral substances are possible depending on local conditions. Those that cause the most common problems in domestic supply water will be discussed here.
Since the beginning of time two important natural processes (weathering and soil leaching) have contributed chemicals to water. Decaying vegetation also adds various constituents and produces mild natural acids that support the soil leaching process.
Man-made causes for dissolved constituents in ground water include all forms of pollution. Disposal of industrial wastes into ground and surface water sources is a contributor to the occurrence of chemicals in water. Chemical fertilizers, petroleum products ("waste oil," gasoline, etc.), pesticides, and synthetic detergents also contaminate some water supplies, as do buried wastes.
Because of the health risks of some chemical substances found in water, the U.S. Environmental Protection Agency (EPA) established drinking water regulations that set limits on the concentration of some substances in public drinking water supplies. These limits are helpful in assessing the quality of individual home water supplies.
Hardness, which is very common in water supplies, is caused by calcium and magnesium in water. Hardness at a moderate level (3 to 7 grains per gallon [gpg] or 50 to 120 milligrams per liter [mg/L]) may be beneficial because water becomes acidic at low hardness levels, which may cause plumbing corrosion or leaching of lead from soldered plumbing joints into the drinking water. Hard water is disadvantageous because soap does not clean efficiently and may leave an insoluble curd on bathtubs, sinks, clothing, and skin. Hard water also deposits a scale inside pipes, boilers, and hot water tanks, reducing their capacity and heat-transfer properties. The condition is commonly treated with water softeners.
Alkalinity is similar to hardness, and is a measurement of your water's overall buffering capacity against extreme pH changes. Its concentration is usually similar to the hardness concentration when calcium carbonate is the main contributing factor to the value. However, if alkalinity is significantly higher than the hardness concentration then the reason may be high sodium in the water. If alkalinity is much lower than the hardness value then the water may be high in chloride, nitrates or sulfates.
Iron compounds, common in rocks and soil, are easily dissolved in water, particularly acidic water. The earth's crust is a major source of iron; consequently, iron exists in many ground water supplies. Water may also contain iron from corroding metal in pipes, pumps, and fixtures.
Small amounts of dissolved iron in drinking water present no concerns, but high levels of iron can cause rusty stains to form on laundry and appliances. Potatoes boiled in iron-rich water turn black, and iron combines with the tannins in tea and coffee to form a black, inky appearance and unpalatable metallic taste. For these reasons, the EPA recommends limiting iron concentrations in drinking water to 0.3 mg/L limit. This value is an EPA Secondary Maximum Contaminant Level [SMCL] guideline (i.e., not legally enforceable by the EPA).
When exposed to air, ferrous iron (dissolved state) oxidizes to ferric iron (precipitated state), which can form an insoluble stain-causing rust. Excess ferric iron creates havoc in plumbing systems, water softeners, and other water-related devices.
Iron bacteria create additional problems. Some iron bacteria utilize dissolved iron during respiration. This may cause a rusty color in water supplies or create a slime that clogs valves, plumbing fixtures, and water-using appliances. The removal of iron can be one of the more difficult tasks in water conditioning. Water softeners can remove iron in its soluble ferrous state if no bacteria are present. Some high-end water softener systems can remove ferrous iron at concentrations up to 25 mg/L. Each manufacturer places a limit on the softener's ability to remove iron. Two common iron treatment methods are catalytic oxidizing filters or oxidation-filtration systems. If iron bacteria are present then chlorination or ozonation may also be required.
Iron and manganese are often reported together because they share similar traits and treatment techniques. Manganese has fewer sources in the earth's crust than iron, but it is present in many natural waters. Manganese-bearing minerals are common in rocks and soils, and may also occur in large concentrations in organic material because it is a plant nutrient. In uncontaminated waters it is usually present at 0.02 mg/L or less; larger amounts of manganese are usually found in acidic waters. Generally, ground water contains more iron than manganese.
Manganese concentrations more than 0.5 mg/L may impart a bitter metallic taste to foods and water and may precipitate to form noxious deposits on foods during cooking and black stains on plumbing fixtures and laundry. As little as 0.1 mg/L of either iron or manganese can stimulate the growth of certain bacteria in tanks, filters, and water distribution pipes. The EPA recommended maximum concentration [SMCL] of manganese in drinking water is 0.05 mg/L, based on aesthetic concerns.
As with iron, manganese may be removed by a water softener if measures are taken to prevent resin fouling. Each manufacturer places a limit on the softener's ability to remove manganese and the water chemistry conditions for most effective operation. When the manganese level exceeds 2.0 mg/L, oxidizing filters or oxidation-filtration techniques may be required but may involve pH adjustment of the water.
Although chloride is only a minor constituent in the earth's crust, it is a major dissolved substance in some waters. High chloride concentrations in water are more common in arid and coastal regions than in humid areas. Chloride in ground water may originate in evaporite rock deposits or from seawater trapped in sediments during their deposition. Other sources of chloride also include solution of dry atmospheric fallout, municipal sewage and industrial wastes, and road salt.
Chloride in excess of 250 mg/L (i.e., the EPA SMCL) may impart a salty taste (Note: seawater has about 19,000 mg/L chloride). In some situations, chloride may accelerate corrosion of pipes, boilers, and fixtures.
The best removal techniques for excess chloride are deionization and reverse osmosis. Most equipment designed for chloride removal also reduces sulfate, alkalinity, and total dissolved solids.
The common sources of nitrate in ground water are farming and lawn fertilizers or the decomposition of septic waste. The presence of nitrates may be especially harmful to those with potential respiratory impairments including the elderly or young children (less than 6 to 12 months old). Nitrates may be transformed into nitrites by bacteria in the digestive tract. Nitrites may then be absorbed into the blood stream. In infant digestive systems, there is insufficient hydrochloric acid to kill nitrite-producing bacteria. Nitrites in the blood stream inhibit the transport of oxygen in the blood stream, which can cause shortness of breath, heart attacks or asphyxiation. Because the condition can create a bluish skin color, it is called "blue baby syndrome" (technically: methemoglobinemia). High nitrate levels are commonly treated with ion- exchange or reverse osmosis systems. The EPA enforceable Primary Maximum Contaminant Level (MCL) for nitrates in public water supplies is 10 mg/L. Boiling water increases the nitrate concentration.
The acid-alkaline character (or pH) of ground water varies by location. Water may be either "acidic" (like vinegar) or "alkaline" (like ammonia). pH values range from 0 to 14. Ground water pH values commonly range between 6.5 and 8.5 (i.e., EPA SMCL). A pH of 7 is neutral. Values higher than 7 are considered alkaline or basic. Values less than 7 are indicative of acidic water. Acidic water is often corrosive, especially if combined with low hardness and low alkalinity. Corrosive water may leach metals (copper, lead, etc.) from water pipes into drinking water, creating a metallic taste. Alkaline water with pH values greater than 8.5 tends to have a bitter or salty taste. The alkalinity level (which is a separate measurement) indicates your water's buffering capacity against extreme pH changes.
Most water treatment systems work more effectively when the pH is near neutral. For this reason, it may be necessary to neutralize the water (correct the pH) before treating it for other problems.
This is a general term for a broad range of hazardous or regulated substances and waste products that are not naturally occurring. They may end up in the ground water supply if they are improperly handled. A few examples of these types of materials include organic compounds (e.g., benzene, MTBE), heavy metals (e.g., cadmium, chromium, lead, mercury, etc.), pesticides and herbicides, polychlorinated biphenyls (PCBs), petroleum hydrocarbon fuels, and polycyclic aromatic hydrocarbons (PAHs).
The treatment of these and similar types of chemical pollution should be considered on a case-by-case, site-specific basis so that the most appropriate solution is implemented. It is important to determine the source of these contaminants before a solution is chosen. Treatment methods may include activated carbon filtration, aeration, ion-exchange, neutralization and others, including combinations of these methods.
In some areas, high fluoride concentrations in groundwater occur naturally. Currently, there is scientific debate regarding the health benefits derived from fluoride in water and the optimum concentration to create the benefits. The EPA SMCL is 4 ppm, but the homeowner should consult a physician and/or dentist to determine what level of fluoride in water would be best. The level is likely to be lower than 4 ppm.
Water treatment to remove fluoride is generally accomplished through specialized and expensive ion-exchange processes that are not discussed in this general pamphlet. Reverse osmosis also is an alternative treatment.
Radon is a colorless, odorless and tasteless radioactive gas. It is formed during the decay of naturally occurring minerals containing radioactive elements such as uranium. Radon gas may enter a home through two primary pathways that include 1) cracks in the foundation and 2) release from the water supply used inside the home.
There is uncertainty among scientists about the health risks related to dissolved radon in drinking water. Currently, the EPA advisory action level (guideline) for radon gas in air is four (4) picoCuries per liter (pCi/L). In 1991, the EPA proposed a MCL of 300 pCi/L for dissolved radon in public water supplies, but this value is under reconsideration by the EPA. A water user can contact local or state health or environmental quality authorities for updates on the permissible levels of radon in air or water.
Radon in water is commonly treated through aeration. Activated carbon filter treatment is not recommended because of the potential build up of radioactivity in the filter as the radon is removed from the water.
The following paragraphs briefly describe the treatment methods commonly used by homeowners to improve water quality. The treatment methods are divided under six categories including filtration, oxidation, ion exchange. ultraviolet irradiation, aeration and pH neutralization.
Filtration simply stated, removes suspended matter from water by mechanical "screening" (Sometimes the word "filtration" is used [incorrectly] to refer to all types of water treatment). Basic filters usually are porous beds of insoluble material. Other examples include cast forms, plates of sheet material, synthetic membranes, finely perforated plastic or specially sized beds of inert particles. Suspended silt, clay, colloids, and some microorganisms are removed by the filtration process. Simple cartridge filters may be effective for low levels of turbidity.
The ability of a filter to efficiently screen Out particles depends on the size of the filter area, the quality of the water to be filtered, the required flow rate of the water, the design capacity of the filter, and its porosity. Filters are generally used for particles less than 0.0029 inches (0.07 millimeters) in diameter.
Filtration, by itself, is inadequate to remove biological contaminants from water. Fine filtration can be a very effective means of particulate removal. It strains out large organisms like protozoan cysts and worm eggs, but should be followed with a chemical disinfection method because some bacterial and viral pathogens may pass through.
Separators are generally used to remove sand or silt from well water. Separators vary in design, but all are in the form of a hydrocyclone. Water is fed at a high velocity into a cylindrical or conical separation chamber, exerting extremely high centrifugal forces on the particles in the water. These particles are forced to the outer walls of the separation chamber and move downward in a spiral path along the wall to the collection chamber. Meanwhile, the clarified water (now free of the particles) moves into the center of the separation chamber and discharges at the top of the chamber. For domestic use, the in-line separator is most common. It can remove up to 98 percent of all suspended solids as small as 0.0029 inch diameters (0.07 millimeters) in water.
Cartridge filters are available in two common types: pleated (sheet-like) fiber or solid (fill or particle-type). Common filter size ratings are 50, 20, 10, 5 and 1 microns (u). The solid types generally will provide more filtering capacity than pleated varieties for a given cartridge volume and filter size.
Activated Carbon Filtration systems involve the adsorption (adhesion) of one material on the surface of a second solid substance based on opposing electrical charges of each material. These systems are widely used to eliminate certain hazardous compounds related to industrial wastes, chemicals and pesticides. This treatment method can also remove unpleasant tastes and odors caused by decaying organic matter, dissolved gases, and residual chlorine. Activated carbon is placed on a filter medium or installed in treatment tanks and adsorbs the taste and odor impurities in water, leaving the water taste- and odor-free. When required to eliminate hazardous compounds (See section "Problem: Industrial Chemicals") the system should be designed by a professional competent to assess the effectiveness of the treatment with regard to the specific hazardous compounds detected in the water. Specific system maintenance plans may be necessary to ensure on-going effective removal of the compounds of concern.
Activated Carbon or Charcoal Filter
Adsorption filtration does not treat microorganisms and should also include a method of chemical disinfection. It is recommended that water be chlorinated before passing through an activated carbon filter. The purpose of the chlorination is to assist in the removal of substances causing taste and odor, and more important, to prevent bacteriological growth on the filter.
Reverse Osmosis methods employ a unit divided into two chambers by a semi-permeable membrane. One of the chambers contains "raw" water with undesirable constituent(s) (e.g., salt). Reverse osmosis involves the application of pressure to the side of the chamber containing the "raw" water. This forces the water to leave the contaminated chamber and flow through the treatment membrane into the "treated" water chamber, leaving the unwanted minerals behind, which are then rinsed to the drain. The membrane filters the water on a molecular scale. Reverse osmosis provides partially demineralized water.
The process is effective for removing many substances, including sulfate and chloride, and it generally leaves the water 90 percent free of mineral and biological foulants. However, pre-filtration or other treatment may be needed for the system to work properly. The removed-substances are disposed of in approximately 1 to 3 gallons of water which are wasted for every 1 gallon that is produced.
Backwashing media beds are used in larger filter tank systems. The tank is filled with an inert (non-reactive), relatively dense material such as sand or ceramic granules. As the untreated water passes through the bed unwanted particles are trapped in the bed. The bed is periodically backwashed to flush the unwanted particles out to regenerate filter space in the bed. In ion-exchange systems, the backwashing process may also regenerate chemicals in the bed that have been used in the treatment process.
Chlorination is used primarily for disinfection. It is probably the most popular oxidizing technique that changes taste- and odor-causing substances into innocuous forms. Because chlorine controls the growth of algae and microorganisms, it is able to reduce the quantity of the taste and odor-causing organisms in a water system. Chlorine also has a residual germicidal action that provides continuing antibacterial protection.
Chlorine is available for domestic water treatment use in solid and liquid forms. Liquid sodium hypochlorite is commonly sold in grocery stores as household bleach. Calcium hypochlorite is the solid form of chlorine and can be obtained as a soluble powder or tablet.
Chlorination equipment is available in three types of units:
Because of the variability of the chlorine demand for domestic water systems, chlorine dosages are usually larger than required; thus, the treated water usually has a noticeable chlorine taste and odor. To eliminate the chlorine taste and odor, an activated carbon filter can be placed after the chlorination system to remove excess chlorine.
Chlorine is the most widely used method in the United States for disinfecting municipal and individual water supplies. It destroys many biological organisms and it meets most of the criteria described earlier in this pamphlet under "Problem: Pathogenic Organisms."
Nevertheless, chlorine has some drawbacks. Chlorinated organics (i.e., certain trihalomethanes) are produced when organic chemicals combine with chlorine in water. Some of these chlorinated organic chemicals are suspected of being carcinogenic. However, these substances occur more often in surface water than in ground water supplies because surface waters have higher concentrations of organic materials. Chlorine's effectiveness can be hampered by turbidity in water. Chlorine will probably continue to be the dominant disinfection method. Homeowners who select a different procedure should first check with state and local health officials to see if such treatment conflicts with any regulations.
Iodine is chemically more stable than chlorine, but more expensive. Iodine disinfection units are not common. They have been used in lunar modules to protect the drinking water of astronauts and for disinfection in remote areas and emergency situations.
Iodination equipment, as with chlorination equipment is installed between the pump and holding or pressure tank and a continuous flow of concentrated iodine is fed into the mainstream of water. This equipment is simple to operate and requires little maintenance. It may, however, impart a slight taste to the water.
Potassium Permanganate is an oxidizing agent that destroys tastes and odors resulting from dissolved hydrogen sulfide gas. Dissolved metallic ions (iron, etc.) which cause taste problems may also be oxidized. Since chlorine and potassium permanganate oxidize soluble metallic ions into insoluble oxides, some filtration method should follow this treatment to remove chemical precipitates.
Ozonation uses ozone as an oxidizing agent. Ozone is an unstable form of oxygen having three atoms per molecule rather than the two atoms typical of atmospheric oxygen. As such, ozone is more reactive than oxygen and is therefore a powerful oxidizing agent.
The ozonation system involves passing dry, clean air through a special form of high- voltage electric discharge. The mixture of air leaving the ozone generator may contain about 1 percent ozone, which is passed through the water to be treated.
In the ozone process, gases and volatile chemicals in water may be stripped by aeration, a process that mixes air and water. Ozonation can strip water of iron, manganese, and sulfur by oxidizing them into insoluble compounds that can be removed by filtration. Ozone can also destroy odor- and taste-producing bacteria. Organic constituents may be oxidized. While this process is used widely in Europe and in industrial applications, it is not commonly used in U.S. residential applications.
This method has a greater germicidal effect against bacteria and viruses than does chlorine. Also, ozonation adds no chemicals to water because it purifies naturally with a form of oxygen. While ozonation does produce residual germicidal power, it is not easily measured. .Ozonation equipment and operating costs are higher than other treatment procedures.
Catalytic Oxidizing Filters can be used when the type or amount of iron exceeds the treatment limits of a water softener. The catalytic oxidizing filter employs a medium that has been impregnated with various oxides of manganese. As ferrous iron-bearing water passes through this filter, the medium oxidizes the iron in the water to form insoluble ferric iron. The resulting rust particles are then trapped in the filter bed. As the rust accumulates, the filter must be cleaned.
This procedure usually removes 75 to 90 percent of the iron, but is only effective at pH 6.8 or above. A water softener should be installed following the filter to remove the remaining iron and any hardness that may be present. Substantial quantities or different forms of iron and iron bacteria can be removed by a water softener or for more severe conditions, by a catalytic oxidizing filter (oxidation followed by filtration).
Oxidation-Filtration may be necessary for adequate water treatment when the iron level in water exceeds 25 mg/L or when high amounts of iron bacteria are present. This process usually involves preoxidizing the iron and removing the precipitated particles with a filter.
Preoxidation is usually accomplished by injecting air or chlorine into the inlet supply line ahead of the pressure or storage tank (Potassium permanganate can also be used as a preoxidation method). The iron oxidizes and precipitates in the tank and is removed by a filter. An activated carbon filter is often used because it removes the excess chlorine, as well as the iron particles, leaving the water odorless and tasteless. Contact time, filter sizes and backwash rates are all critical variables for effective treatment.
Oxidation-filtration is widely used to control iron bacteria. When these bacteria are first detected, shock chlorination (an injection of chlorine about 10 times larger than the dose used in regular chlorination) is recommended prior to the installation of water conditioning equipment. When extremely high iron levels are present, some equipment may need to be doubled (i.e., repeated in the treatment sequence to increase contact time or treatment time) for thorough treatment.
Water Softening is based on the ion-exchange process and employs a tank containing a bed of insoluble material. This material (a resin) has a negative charge with positively charged sodium ions attached to it. With most water supplies, the resin has a stronger affinity for calcium and magnesium ions than for sodium ions. Thus, when water containing calcium and magnesium passes through the resin, the hardness ions are attracted to the resin and the sodium ions are released in an equivalent quantity to the water supply. In essence, the water softener trades sodium ions for calcium and magnesium ions; hence the term ion-exchange. The total ionic content of the water does not change.
Ion Exchange/Water Softener Mineral Tank
When all sodium ions are displaced, the resin becomes exhausted and must be regenerated by passing a strong sodium chloride solution (brine) through the resin during a backwash process. Sodium ions are placed on the resin while hardness ions are washed to the drain with the spent brine. This reversal of the sodium/hardness preference is caused by the strength of the regenerative brine.
Persons on low-salt or low-sodium diets should consult a physician before regularly drinking softened water. In normal situations, the added salt from drinking softened water is a small fraction of salt that is consumed from foods.
Although a water softener has some filtering ability, water with heavy turbidity or particulate matter should be filtered prior to softening. A water softener can remove limited quantities of certain forms of iron, but it should never be used alone when the water is red or rusty (indicating precipitated iron) or when iron bacteria are present.
A water softener is not the only means of combating hardness. Where a water softener is impractical, certain polyphosphate compounds can be added to the water supply with a chemical feeder to alleviate some hard water problems. While such treatment in no way provides all of the advantages of soft water and does not inhibit the formation of a soap curd, it can help curb scale formation within the hot water system.
Dealkalization is very similar to water softening except that a different ion exchanger is used that can exchange chloride ions for sulfate ions, leaving the water free of sulfate.
Dealkalization will also reduce the alkalinity level of a water supply. A 70 to 90 percent reduction in both sulfate and alkalinity can be expected from this system if properly used. It should be noted, though, that the resultant chloride content of the water might exceed the 250 mg/L EPA recommended limit SMCL for chlorides.
Deionization also known as demineralization, involves the removal of all ionized minerals and salts from a solution by a two-phase, ion-exchange procedure. Positively charged ions are exchanged for a chemically equivalent amount of hydrogen ions and negatively charged ions are exchanged for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions then unite to form water molecules, leaving the treated water free of all ionized contaminants. This treatment is normally only used for commercial or industrial applications.
Ultraviolet light provides bacterial killing action much the same way sunlight helps kill bacteria. The ultraviolet unit consists of one or more ultraviolet lamps usually enclosed in a quartz sleeve, around which the water flows. The lamps are similar to fluorescent lamps, while the quartz sleeve surrounding each lamp protects the lamp from the cooling action of water. The killing effect of the lamp is reduced when the lamp temperature is lowered.
Water passes in a relatively thin layer around the lamp since the germicidal action of ultraviolet irradiation depends on the intensity of the light, depth of exposure, and contact time. Water flow must be regulated to ensure that all organisms receive adequate exposure. Turbidity and minute traces of iron compounds reduce the light's transmission. Therefore, the water should be pre-filtered so that untreated organisms do not slip by.
Ultraviolet irradiation units are automatic, require little maintenance, and do not add undesirable materials to the water. However, these units offer no germicidal residual, so that determining the system's effectiveness is difficult.
This process treats water through intimate contact with air. Aeration may be accomplished through several methods including spraying, cascading, aspirating or bubbling the water supply to bring it in direct contact with air. Either pressure (closed system) or gravity (open system) aerators may by used. Pressure systems are used primarily for oxidation while gravity systems are commonly used for degassing (e.g., removing dissolved radon, carbon dioxide, hydrogen sulfide or methane).
In order to increase the overall efficiency of a water conditioning system, acidic water may be pre-treated by passing it through a tank containing a bed of granular lime, calcium carbonate or marble before entering the remainder of the treatment process. Similarly, alkaline water may be treated with an acid drip or injection process to neutralize the water.
The American Ground Water Trust, State health departments, water well construction agencies, local health officials or ground water industry professionals are sources for assistance and/or referral to qualified water testing services.
It is important to have an independent water analysis. Don't rely solely on a "kitchen test" from a water conditioning equipment salesperson. While many water conditioning sales people are trained in water chemistry, some are not. Look for a professional who understands your water chemistry, explains your treatment options and who pays attention to the details specific to your home and water supply. Before purchasing major conditioning equipment, obtain information and bids from more than one conditioning company. You may want to check on the reputation of the company by contacting your local Better Business Bureau.
Most state health departments maintain a list of certified water testing laboratories. In some areas, a public agency (often a county health office) may perform basic bacteria and nitrate analysis at little or no charge. Some certified laboratories offer nation-wide water testing via mail/courier service. If extensive chemical analyses are required or preferred, or if unusual chemicals in low concentrations are suspected, the homeowner will need the services of a certified laboratory.
"Do-it-yourself' water testing kits are available in many hardware stores. These kits provide a quick convenient test for homeowners but will not have the accuracy of a laboratory test and the results may not be accepted for purposes such as property transfer water quality tests. If there is an immediate health issue, such as gastrointestinal illness, a local or county public health department, sanitarian or county extension agent should be consulted and water testing done by a certified laboratory.
A reliable water sample is of utmost importance. Homeowners who must obtain the water sample themselves should request written instructions and sterile sample bottles from the laboratory or agency performing the analysis. Following the correct "sampling protocol" is vital for an accurate and meaningful water quality analysis.
A laboratory may report the quantity or concentration of a substance in a water sample using several different labels or units. Common units of concentration include parts per billion (ppb), parts per million (ppm), micrograms per liter (µg/L), milligrams per liter (mg/L) or grains per U.S. gallon (gpg). Similarly, filters are offered with various spacing (opening) sizes that may be listed in inches, centimeters (cm), millimeters (mm) or microns (µ). Converting between these units may be performed using the following information:
|1 ppm||=||1,000 ppb||1 ppm||=||1 mg/L|
|1 ppb||=||1 µg/L||1 gpg*||=||17.1 mg/L|
|1 inch||=||2.54 centimeters (cm)||1 cm||=||10 millimeters (mm)|
|1 cm||=||0.393 inch||1mm||=||1,000 µ|
|1 liter (L)||=||0.264 U.S. Gallon (gal)||1 gallon||=||3.785 liters|
|1 gal/minute||=||0.0758 L/second||1 ounce||=||28.3495 grams (g)|
|kilo (k)||=||103||milli (m)||=||10-3|
|micro (µ)||=||10-6||pico (p)||=||10-12|
* Clark Hardness as calcium carbonate (CaCO3) by weight
Information in this pamphlet is provided in good faith to inform the public about ground water and ground water related issues. In all cases, the Trust urges consumers to contact local experts, and where appropriate, to refer to local codes, rules, regulations and laws.
|America's Priceless Ground Water Resource - An introduction for the homeowner to the occurrence of ground water in the hydrologic system.|
|Septic Systems for Waste Water Disposal - This pamphlet explains how septic systems work.|
|Water Conservation In Your Home - Offers practical suggestions for conserving water resources and reducing the use of energy.|
|When You Need A Water Well - Guidance on making good economic and environmental decisions about water wells and choosing a professional well contractor.|
|Rural Drinking Water - Private Wells or Public Water Supply - Water supply decisions should be based on properly planned cost-benefit studies. This pamphlet offers a checklist guide for citizens.|
|Bacteria And Water Wells - Describes the natural occurrence of bacteria beneath the ground, how wells may be affected and how to fix them.|
|Ground Water - A Source of Wonder - The basic geology of ground water and related issues for middle school student science programs.|
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