The water in municipal water supplies is treated with chlorine because

Long Answer:

We put chlorine in our water because we want to be protected from bacteria. The chlorine keeps our water clean and nice and blue. If you have green water then it is time to get an enhancement of chlorine. Another reason we put chlorine in our water is so all the bugs that try to stick on us beneath the pool do not have a chance because they go to the surface and away to the skimmer. The last reason is, because we need to keep things away like dirty items that land in the water so we do not touch the water and get sick.

Short answer:

We put chlorine in the water so we are protected from bugs and dirty things in our pool. Chlorine also keeps the water nice and blue so we know that it is clean.

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