An abundant source of water!
A 1982 study by the United Nations Environment Program showed that, in an area with an average rainfall of 72 inches, 12 hours of rain provided enough water to serve a family of 6 for 45 days. That’s a lot of water!
Rainwater was a common source for drinking water in rural areas of the US until the 1920’s. Below is a diagram for a modern rainwater collection system with debris filters for drinking purposes.

Thank you to RainwaterConnection for the excellent diagram, and here is some excellent research from the United Nations Environment Program in Japan.