Water treatment is the process of cleaning water. Treatment makes the water safe for people to drink. Because water is a good solvent, it picks up all sorts of natural pollutants. In nature, water is not always clean enough for people to drink. When the microscope was invented in the 1850s, germs could be seen in water for the first time. In 1902, Belgium was the first country to use chlorine to clean or treat water in a public water supply. Today, almost every city in the world treats their drinking water. Treatment includes disinfection with chlorine or other chemicals to kill any germs in the water.