We've never run out, and we've been living off tank water for one hundred years here. This is for the house, the dairy is another matter as it uses alot more water for cleaning etc. It usually runs out in years of drought (two of the last five years we've had to buy in water). It always fills to overflowing during the wetter months though, so if we just put in more storage then we probably would survive the bad years too.Not really. The hard bit is catching it in large doses. And if the fresh water doesn't fall from the sky, you're screwed. I know people who have had to live entirely off tank water and it is amazing how much rain you need on your roof to keep up the supply.