Chlorine - A Special Problem
for Drinking Water
"There is increased evidence for an association between rectal, colon and bladder cancer and the consumption of
chlorinated drinking water", this according to the President's Council on Environmental Quality.
Why Use Chlorine? Chlorination is used extensively by municipal water treatment
plants to disinfect water. However, the gaseous chlorine used by these plants is much too dangerous for home use.
Household bleach (a 5.25% solution of sodium hypochlorite which is equivalent to 5% available chlorine) can be used
for disinfecting drinking water (How to Super Chlorinate). When chlorine is fed into water, it first reacts with
any iron, manganese, or hydrogen sulfide that may be in the water. If any residual (un-reacted) chlorine remains it
will next react with any organic material (including bacteria) present. In order to ensure that the water remains
protected throughout the distribution system, an excess of chlorine, usually .5 parts per million (ppm) is added.
In large systems chlorine will be added again at distribution junctions. This "rate of feed" is normally adjusted
to make sure that sufficient chlorine is available to fully react with the organics present. When both the mineral
and organic reactions have been completed, any residual chlorine remains in the drinking water. Most people find
the taste of water with residual chlorine to be objectionable but they do get used to it! Chlorination kills many
pathogenic bacteria (including those which cause typhoid, cholera and dysentery), however cyst-forming protozoa
(Cryptosporidium), which cause amoebic dysentery, and giardiasis, are extremely resistant to chlorination.
So What's the Problem? Chlorine as stated above is a very effective disinfectant
and has been used in drinking water supplies for nearly 100 years. What concerns health officials are the
chlorination by-products, "chlorinated hydrocarbons, “known as trihalomethanes (THM's). Most THM's are formed in
drinking water when chlorine reacts with naturally occurring substances such as decomposing plant and animal
materials. Risks for certain types of cancer are now being correlated to the use of chlorinated drinking water.
Suspected carcinogens make the human body more vulnerable through repeated ingestion and research indicates the
incidents of cancer are 44% higher among those using chlorinated water.
To minimize the risks of using chlorine, the EPA (Environmental Protection Agency) adopted new regulations in
November 1980, requiring cities to cut down the chlorination by-products in water to a level not exceeding 100
parts per billion. Dr. Robert Harris, an environmental scientist and one of the three members of the White House
Advisory Council, said that while this new reduced level is a beginning, but it still doesn't provide proper
safeguards and should be strengthened. Dr. Harris recommended that citizens find out the current levels of
chlorinated by-products in their drinking water and if necessary buy bottled water or home purifying systems. Yet,
there is little likelihood that the use of chlorine will be discontinued since it is currently the MOST
ECONOMICALLY acceptable chemical for bacterial control at this time.
It is ironic that chlorination, the very process by which we cleanse our water of infectious organisms, can
create cancer-causing substances from otherwise innocent chemicals in water. Cancers of the kidney, bladder and
urinary tract are more common in certain cities than others; why? New Orleans takes its tap water from the highly
polluted Mississippi River and adds chlorine in excess of government standards to insure protection against
infectious diseases. Approximately 63 new carcinogenic compounds are created in Mississippi drinking water when
chlorine combines with methanol, carbon disulphide, and other substances.
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