This article, written by the American Ground Water Trust was originally published in THE AMERICAN WELL OWNER, 2003, Number 1


"Hard" water has high levels of dissolved calcium and/ or magnesium minerals. These minerals may occur in ground water passing through limestone rocks, or other rocks with a calcium mineral content. The level of hardness is related to the amount of dissolved mineral in the water. Hard water does not pose a health risk but it can cause "scale" (mineral build up in pipes and plumbing fixtures) and reduce the effectiveness of soap for bathing and laundry. Clothes washed in hard water may not feel soft because the soap does not rinse out properly, dishes may have spots when they dry, and bathroom surfaces may be difficult to clean. A clear sign of hard water is the build up of scale in a kettle. An additional place for the build up of scale is in the hot water heater. Over time, scale accumulation can lead to inefficient water heater operation requiring more energy (and more expense).

Water hardness levels can be established by a laboratory and are measured in milligrams per liter (mg/l) but may also be reported in the archaic form of grains per gallon. [One grain of hardness equals 17.1mgl] Typical water hardness classifications are:

Soft water Slightly hard Moderately hard Hard Very hard

less than 17mg/l 17- 60 mg/l 60-120 mg/l 120-180 mg/l 180 + mg/l

Hardness at a moderate level of 50 to 120 mg/l may be beneficial because water could become acidic at low hardness levels, which may cause plumbing corrosion or leaching of lead from soldered plumbing joints. (New homes should have lead-free solder). Most household hard water problems are solved by the installation of point of entry (POE) equipment. These water-softening units are permanently installed into the home's plumbing system. Water softeners are the most frequently used of all water-conditioning devices and are installed for reducing hardness for private wells and utility supply with high levels of calcium or magnesium.

Most water softeners operate by ion exchange. In this process, the hard water is passed through a cylinder filled with resin beads that have been saturated with sodium. This resin beads have a negative charge, with positively charged sodium ions attached and have a stronger affinity for calcium and magnesium ions than for sodium. When water containing calcium and magnesium passes through the resin, the hardness ions are attracted to the resin and the sodium ions are  urgently released. The water softener trades (exchanges) sodium ions for calcium and magnesium ions; hence the term ion-exchange.

Approximately one mg/l of sodium is released for every two mg/l of hardness that is "trapped." When the beads become saturated with calcium and magnesium, the softening cylinder is recharged with sodium by passing a very salty brine solution through the resin beads. The sodium in the brine then replaces the calcium and magnesium that are then discharged as wastewater into the septic system or sewer.

Water softeners may regenerate automatically on a time basis, on a volume of water used basis, or by a sensor on the output side of the system. Large capacity softeners will regenerate less often. There are many water softening devices available. There is NOT a one-size-fits-all water-softening device. When selecting equipment there are other factors such as the iron content of the water that could influence performance.

In normal situations, the added sodium from drinking softened water is a small fraction of sodium that is consumed from foods. However, people who may be at risk from ingesting too much sodium may want to have an "unsoftened" water line to the kitchen for cooking and drinking. A sodium based softening system removing 180 mg/l of hardness will add about 80 mg/l of sodium. A non-sodium option is to use potassium chloride.

Some water softening equipment makes use of uses added chemicals to reduce water hardness. So called precipitating water softeners may use washing soda and borax and non-precipitating water softeners use phosphates. 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.

For more information about water softeners visit.www.wqa.org. This Water Quality Association website has information about conditioning equipment available in North America.

[© American Ground Water Trust. This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 2003, Number 1]