If I walk around to the back of my house, there is a 600 gallon water tank with two downspouts from a rooftop deck draining into the covered and screened top. When I last checked, it was full to the brim. Water is drawn out of the bottom of the tank via a standard garden hose faucet.

When I lived in Iowa 42 years ago, I had the same arrangement on my farmhouse, except the tank was an underground cistern with a handpump on it.