Chlorine has a strong impact on guarding  water supply for over 100 years. Chlorine is a cheap disinfectant. That's why municipalities use it.

Chlorine is considered the most effective means to remove pathogens, including microorganisms, infections, and protozoans that can develop in our water supply.

So, nobody opposed that chlorine fills an urgent need.

There is pollution, and different kinds of harmful wastes are being thrown in some bodies of water. You can only imagine what kind of toxic substances can be floating in the water. This water is what you drink, and you use it to clean your body with and wash your clothes and dishes with.

Water companies know how dangerous raw and untreated water can be. So they started using some agents to disinfect the water.

It is chlorine.