I live in Australia and we're going through a nasty drought right now. The government has us on water restrictions similar to rationing. Scary?
It's law now that all new houses built in our state must have a rain water collection tank plumbed to run the toilet cystern. It didn't cost that much and it's a great idea.
I personally have two rain water collection tanks at my home - one to run the toilet and the other to water the gardens, wash the car, fill up the bucket when cleaning floors, wash the dog, wash the windows...
Who says you can't use rainwater?
Raven