Because your body is a "natural" water filter. The human body collects, processes, and filters contaminants on a daily basis from the food, water and air that we consume. If you drink water with high levels of pollutants, your body then becomes a living filter of sorts. It will remove many contaminants on its own but whatever it cannot remove will be left behind to be absorbed or deposited in your tissues and organs. Over time, the accumulation of toxic contaminants could overwhelm your body's natural defenses leading to serious disease, cancer and death.

It is easy to replace a bad cartridge with a new one when a water filter fails. It is much harder to replace any valuable organs when the human body fails.

Don't use your body as the filter!