[Cob] rain water

[Jilly]

Collecting rain water in the NW is certainly no problem. While the number if inches - around 48, per year is similar to that of NYC, the rain is more constant. 
Although I have a family member living in AR, with a metal roof. There is a collection tube around the circumference, that leads to under ground storage tanks (3 of them). Once a month he puts in something like Chlorine - very small amount. And there is some kind of filter before it runs into the house. He has never run out of water, and has a family of 4. I don't think it rains there as much as here, but maybe when it does, it pours.. I am not sure. 
jill