Why is the "chlorination" method of purifying water controversial?
Chlorination is the process of adding chlorine (bleach) to water in order to kill contaminating bacteria, making it drinkable. This is a very common form of purification, mainly because of the ease and high-success rate; it is simple to add a bottlecap of bleach to a gallon of water and let it sit for an hour. While the taste is classically "pool-like," the water will be safe to drink. However, there is an opinion that chlorine, being a very toxic chemical, can build up in the body and cause disease and other problems; it has even been implicated in causing cancer over long-term use. At the moment, most of the evidence points to small amounts of chlorine, entering the body on an irregular basis, being safe; hikers and those living in third-world countries have used bleach to purify water for decades without much trouble. The most common problem is using too much; a small amount of bleach will purify water over time, as long as it is allowed to sit with intermittent agitation. However, chlorine can also build up in the environment, harming plants and wildlife that cannot filter it as efficiently as humans. Chlorine can also react with non-organic molecules to form Disinfection Byproducts, which may be carcinogenic. The debate and studies are continuing.