Chlorine is added to drinking water worldwide to ensure safe, disinfected drinking water, after all diseases which can cause severe illness and death are less than desirable.

Easily prevented diseases from poor quality drinking water is still a leading cause of death worldwide.

The New Zealand Drinking water standards set out a maximum allowable value of 5mg/L of chlorine in drinking water, measured as free available chlorine. WIth a note that disinfection must never be compromised.

However, many people dislike the taste and smell of chlorine in their drinking water and prefer to remove it before drinking.

In addition to this, when chlorine disinfects water which also contains organic matter such as humic and fulvic acids, byproducts called Trihalomethanes (Commonly called THMs) are formed. THis is much more common in surface water sources, which tend to have higher levels of organics.

Trihalomethanes (THMs)

Trihalomethanes include bromoform, bromodichloromethane,chloroform and dibromochloromethane.

Most of the studies have been done on chloroform.

It has been shown that drinking chlorinated water, absorption through the skin and inhalation by showering in chlorinated water contribute significantly to exposure.

Short Term/Acute Exposure (at high levels)

In addition to central nervous system effects, chloroform anesthesia was associated with cardiac arrhythmias and abnormalities of the liver and kidneys. Inhalation exposure experiments with animals revealed that high levels are toxic to the liver and secondarily to the kidneys. Skin contact with undiluted chloroform may cause a burning sensation, redness, and blistering.

Long Term Exposure

Long term or chronic oral exposure to chloroform at high doses results in adverse effects on the central nervous system, liver, kidneys and heart in humans.

Animal studies have shown decreased body weights in rats and mice who werw given chloroform at high oral doses. These studies have also shown increased incidence of respiratory disease at higher doses.

At very high doses given orally, liver abnormalities and decreased size of the reproductive organs were observed in rats. In animal studies investigating effects of chronic exposure to each of the other THMS, liver toxicity was observed. BDCM also caused kidney toxicity.