Re Rajasegar's comment: THMs ...

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Re Rajasegar's comment: THMs are NOT carcinogenic in lifetime  animal studies dosed  in water. Starting with chloroform, they did give tumors is the older rat and mouse studies dosed in corn oil.  This has been known for many years, The last lifetime study on bromodichloromethane in 2006 at 700 mg/L gave NO tumors.  So, the cancers were an artifact of the test  design. WHO Guidelines are based upon non carcinogenicity effects at high doses.

Many water people are not up to date on the science.

I am about to publish a study in Dose-Response Journal of bladder cancer incidence in 8 countries since THMs were discovered and regulated- ( I wrote that regulation in the US while at USEPA)-over 40 years. The bladder cancer incidence rate has been flat--no change.   In the US and Canada where THMs are about 1/3 what they were in the 1970's ,

So, use chlorine judiciously. It's easy, and cheap and it works.