Water is the source of life as we know it. Three quarters of the Earth is covered with water, and our bodies are made of a similar percentage of this wondrous compound. For millennia, our ancestors drank from streams, pools, springs, and puddles, often falling sick or dying from unseen contaminants. Through trial and error, we learned which sources were safe and which were hazardous, but not until the mid-1800s, during yet another London cholera epidemic, did scientists clearly connect sanitation and waterborne disease.
