This article, written by the American Ground Water Trust was originally published in



Virtually all public supplies are chlorinated.  Why do public supplies need chlorination when private wells don't?  One of the major benefits of on-site well water supply is that water treatment is rarely needed for health purposes.  (Conditioning equipment for water softening and iron removal are fairly common in homes, but are undertaken for aesthetic rather than health reasons.)  Well water can come from deep underground to the tap in minutes.  If the aquifer is safe and the well properly constructed, there is virtually no opportunity for micro-organisms to get in the water.


Any raw water supply source from lakes or rivers will contain organisms.  Chlorine is used to remove micro-organisms from water.  Water supplied via pipelines may spend days moving through the system before it gets to the consumer.  Chlorine added to the water will reduce the chance of micro-organisms multiplying in the pipes or storage tanks.  The art of the water treatment plant operators is to add enough chlorine to fix the risk of micro-organisms, but not to add too much so that consumers complain about the yucky smell and taste of the chemical.  Disinfection by chlorine has been standard practice for nearly a hundred years.  The use of chlorine as a disinfectant has saved hundreds of thousands of lives by making drinking water safe.


The current public debate about chlorination concerns the direct health impact from ingesting chlorine and the by-products that may be formed in chlorinated drinking water. There are reports that indicate that free chlorine causes fats to form cholesterol deposits that may clog arteries. Chlorine can also destroy beneficial vitamin E.  Vitamin E prevents the formation of free radicals (destructive molecules that promote tissue breakdown and tumor formation).


One class of chemical compounds formed as disinfection by-products is called trihalomethanes.  While there are animal studies linking these chemicals to an increased risk of cancer, there is controversy about whether there are statistics to link human health risk to chlorine and chlorination by-products.


Overall, the proven immediate health benefits of chlorination would seem to far outweigh any long term risks.  The debate continues.  Fortunately for most well owners this is an issue that does not affect them directly.



[© 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, 1998, Number 4]