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Chlorine level in Manchester tap water being brought back to normal

New Hampshire Union Leader

September 12. 2013 10:50PM

MANCHESTER — Water Works has begun ratcheting down the levels of chlorine in tap water, after more than a month of higher chlorine concentrations to combat high levels of coliform bacteria, a Water Works official said.

Director David Paris said city water users who noticed chlorine smells or tastes should see a change in the coming weeks, once the usual disinfectant is re-introduced and makes its way through the system. A reduction in bacteria levels and cooler water temperature have allowed Water Works to return to its usual disinfectant, he said.

The higher cholorine level has been in effect since mid-July, when tests detected higher-than-normal counts of bacteria, he said.

At that time, officials brought cholorine up to 2.5 parts per million of water. This week, they reduced it to 2.25 parts per million, and next week it will drop to 2 parts per million.

After that, Water Works plans to shift to its usual disinfectant, chloramine, a chemical composed of chlorine and ammonia. The chemical is not as effective in killing bacteria, but lacks the taste and odor problems of straight chlorine, Paris said.

Also, it does not have the health consequences of chlorine. Chlorine can combine with organic matter and form potentially cancerous material.

Water Works started using chloramine as a secondary disinfectant in 2006. It is added to tap water at a concentration of 2.5 parts per million.

Chloramine is four parts chlorine, one part ammonia.

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