Logic or Not

Now this defies logic. I received some junk mail today from this company selling rain water tanks. It read "Dear Mr Martin" I'm assuming BBC sold my name and address to them on some database. Anyway the crux of the advert read, " Did you know that level 3 water restrictions may come into effect in the very near future, due to Brisbanes lack of rainfall ? It's important we all in these trying days need to be able to conserve water and one way this can be acheived is to install a rainwater tank on your property. You may qualify for a rates subsidy from the Brisbane City Council if you were to do so. One of our trained consultants can visit you to discuss your needs" etc, ect... Now this is the bit that defies logic, how can i conserve water if we have no rain how will it fill up?