Water from public water supplies has been disinfected with chlorine for over 100 years. There is no doubt that that such disinfection has reduced the occurrence of water-borne disease and helped save thousands of lives. However, over the past 30 years there has developed a body of evidence that chlorination of drinking water results in the formation of a family of toxic substances known as chlorinated hydrocarbons. Members of this family include chloroform, chloroacetic acid, and chlorinated phenols. Most of these chemicals are persistent in the environment (they do not biodegrade), and have known toxic effects (carcinogenicity and reproductive toxicity).

The EPA and regulatory agencies in most other developed countries set strict maximum levels (typically in the part-per-billion range) on chlorinated hydrocarbons in drinking water to protect the public. Public water supplies are required to test their water for chlorinated hydrocarbons and report the results of testing to every household they supply. Thus, this information should be available to you.

Drinking water directly from a hose creates another set of issues. Monomers and degradation products from the rubber may contaminate the water, and chlorine in the water may react with these to create additional chlorinated hydrocarbon contaminants. The unique taste of water from a rubber hose is a rite of summer, but it should also be a warning that you are drinking more than the water you expect.