There are various methods to purify water. These methods include reverse osmosis, solar treatment , distillation etc. The purest form of water available is from rainwater. But nowadays due to increase in air pollution and atmospheric pollution levels and acid rains, this water needs to be treated . Using impure water causes diseases like cholera , jaundice etc. It is necessary to drink water it is also more necessary to consume pure water. Natural treatment methods consists of different techniques
Most common is boiling
Boiling water would destroy the bacteria and other disease causing organisms.
Distillation
Keeping impure water with non soluble content stagnant for some time helps the high density particles to settle down
Other methods include different levels of filtering using sand charcoal etc.