The experimental use of chlorine began in the 1890's to combat water-borne diseases such as cholera and typhoid. It quickly gained widespread acceptance because of its low cost and high efficiency in killing just about everything hazardous in water.

The problem with chlorine is that it is a known toxin and the implications of drinking this toxin over the long-term (i.e. your lifetime) is highly uncertain. Chlorine disinfection of water works by the formation of Hypochlorous and Hydrochloric acid. It is an extremely reactive substance and may also chemically bond with other substances in water, depending on the conditions to form further toxins. For example, it is known that chlorine reacts with naturally occurring phenols in water (which are naturally produced by plant life in water) to form Chlorophenols which are highly toxic to all aquatic life.

Chlorine also combines with other natural organic substances to form potent, cancer causing compounds known as Trihalomethanes (THMs). Trihalomethanes include such carcinogens as chloroform, bromoform, carbon tetrachloride, bischloroethane and others. The amount of THM's in our drinking water is theoretically regulated by the EPA. Although the maximum amount allowed by law is 100 ppb,(parts per billion) a recent study showed 31 of 112 municipal water systems exceeded this limit.

Many believe that Disinfection By-Products (DBP's) are the single greatest threat in our water supplies, risking both human health and our aquatic environments. DBP's are contaminants, most of them cancer causing, that are left behind by the very chemical (chlorine) that is used to make water drinkable. Trihalomethanes are associated with an increased risk of bladder and rectal cancer, possibly accounting for 5,000 new cases of bladder cancer and 8,000 new cases of rectal cancer every year in the United States. Other disinfection by-products can cause adverse effects on the liver, nervous and reproductive systems.

Over 2100 contaminants have been detected in U.S. drinking water since 1974 with 190 known or suspected to cause adverse human health effects. In total, 97 carcinogens and suspected carcinogens, 82 mutagens and suspected mutagens, 28 acute and chronic contaminants and 23 tumour promoters have been detected in U.S. drinking water. The remaining 90% of the organic matter present in drinking water has not been identified to date.

Approximately 230 million Americans (that's 90% of the population!) drink chlorinated water which also could contain hundreds of disinfection by-products. A new study on cancer risks in chlorinated water conducted by the Ontario Treatment and Research Foundation and the University of Toronto found:

• Long-term consumption of chlorinated water increases the risk of bladder and colon cancer. Between 10% to 13% of all bladder and colon cancer in Ontario may be attributed to disinfection by-products in chlorinated water.
• There is a 60% increase in the risk of bladder cancer for people exposed to high levels of disinfection by-products for more than 35 years as compared to people with little or no exposure.
• Long-term drinking and bathing in chlorinated water likely causes a 34% increase in the incidence of bladder and colon cancer. The risk increases with the length of exposure and the concentration of disinfection by-products in the water.
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THM's are a big pollutant because of the amount of chlorination used They are a separate class of chemical from chlorine itself. Just because a drinking water system removes chlorine does not mean that it will remove THM's.

In the last 60 years more water authorities world wide have been combining Chlorine with Ammonia when treating water supplies which creates Chloramine. Chloramine, whilst less toxic than chlorine is a very stable substance and therefore provides long term disinfection properties whereas chlorine is quickly dispersed. Chloramine is more difficult to remove from your water supplies than chlorine and is still very damaging to aquatic life.

At low levels, chlorine and chloramine will stress your koi, burn fins and gill tissues and strip mucus. They will also cause irreparable internal organ damage.

Safe levels of chlorine and chlorine derivatives in water for fish life are less than 0.10mg/litre according to the EA in the United Kindgom.

The message is clear -

• Ensure that when you top up your pond you do so via a purifier utilising activated carbon

• Always use a dechlorinator when adding water to your pond, even if you use a purifier.

• Test your water for the presence of chloramines – especially during the summer when chlorination levels are increased.

• Stop drinking water and drink more beer!