The Advantages of Using Rainwater

Rainwater is relatively pure stuff. The process of evaporation leaves chemicals behind, and what you see falling from the clouds starts out pretty clean. It picks up particulates, pollution, pollen and dust as it makes its way to the ground, but even those contaminants become less of an issue if it's been raining for a while and the air is cleaned with a good water scrubbing....http://home.howstuffworks.com/rain-barrel1.htm