Why chlorine in drinking water is a concern?
Chlorine is a powerful oxidant.

What is oxidant?
An oxidant attacks a molecule and steel the electron from the molecule.

Or may be it is easier to understand if we think of antioxidants which we are more familier with. Antioxidant shares or donates his electrons to other molecule and he is a good guy. So, oxidant is a bad guy.

Because of this powerful oxidant properties, chlorine is used to kill bacteria. Chlorine is a bad guy to bacteria because it kill it by attacking the important proteins in the bacteria.

The presence of chlorine in municipal water is for reducing the risk of water borne diseases. It is added during treatment of our tap water. Chlorine is effective against a wide range of patogens including bacteria and virus. However, it is not effective against protozoan cysts such as Cryptosporidium.

We know that chlorine can kill bacteria. So, how would it affects our health? How chlorine attacks our body cells is the same as how it attacks bacteria. This cause our tissue to damage and causing chronic inflammation.

During water treatment and distribution of municiple water, chlorine interacts with organic matter in the water. This will form halogenated by-products such as trihalomethanes (THMs), haloacetic acids, haloacetonitriles, chlorophenols and chloral hydrate. Trihalomethanes are chloroform, bromoform, bromodichloromethane and chlorodibromomethane.

Three of the THMs i.e. bromoform, bromodichloromethane and chlorodibromomethane are carsinogens. They increase the risk of bladder cancer, colon cancer and rectal cancer. The halogenated by-products can increase the risk of specific birth defects too.

The highest chlorine levels in drinking water allowed:

  • Chlorine – 4.0 mg/L

The highest levels of chlorination by-products in drinking water that allowed :

  • Haloacetic acids – 0.060 mg/L
    • Dichloroacetic acid – zero
    • Trichloroacetic acid – 0.02 mg/L
    • Monochloroacetic acid – 0.07 mg/L
  • Total Trihalomethanes (TTHMs) – 0.080 mg/L
    • Bromoform – zero
    • Bromodichloromethane – zero
    • Dibromochloromethane – 0.06 mg/L
    • Chloroform – 0.07mg/L

Source : US Environmental Protection Agency

Whenever we wash our food using chlorinated water, the free chlorine that presents in the water will react with the food (organic matter). This will produce THM too. Therefore, thoughout our life, the THM intakes to our body is not only from drinking water but also from the food that we eat prepared from chlorinated water.

Besides of the health effects, high doses of chlorine in drinking water can give undesirable smell and taste.