Rainwater harvesting is one of the oldest and most effective forms of water collection. It is also a key to decentralizing the water supply, removing your reliance on a community pool that can be cut off or contaminated in emergencies.
The process is about as simple as it sounds. Catch the rain on a roof and drain it into giant tanks. The water can be used for any water purpose and, with treatment, can be consumed safely.
Rainwater collection facilities can range from simple, like catching the water off your roof in tanks with spigots, to complex, like integrating it into a building's plumbing. The average 25'x40' roof can catch 600 gallons of water in an hour!