Chlorine bleach in the form of chlorine dioxide is added to practically all U.S. public water supplies as a disinfectant. It is not used because it is safe, but because it is cheap. Adding chlorine limits the liability of the governmental agencies who provide potentially putrid water, because the side-effects of their chlorine disinfection are difficult to trace and occur only after extensive long-term use. For example, it would be easy for citizens to prove that they became ill from drinking non-disinfected water by simply testing the contaminated water for live pathogens, but it is much more difficult to prove that their heart disease or cancer was created by chlorine by-products after twenty years of consuming it. Chlorine bleach is used to satisfy certain priorities, whereby saving money is a much higher priority than long-term public health. When usage of chlorine began in the early 1900's, the long-term effects were unknown, but there are no longer any legitimate excuses that could be used to justify forcing the public to drink bleach. It is not uncommon to find the chlorine in tap water at such a high level that it is unsafe for swimming pools. A simple chlorine test kit from a local retailer will typically yield surprising results.