The rainwater catchment system at Humboldt State University in California is based on collection of rainwater and gravity flow pressure principles. Rainwater runs off the roof of the Buck house into rain gutters. The gutters channel the water and empty it into a standpipe. When the standpipe has reached its capacity of 150 gal, the overflow runs through a pipe and empties into a 900 gal drum. Two 300 gal barrels collect the overflow from the 900 gal drum and any other overflow drains to the public sewer system.
Spigots are built into the bottom of the standpipe and the 900 gal drum. The pressure of the water in the standpipe and the drum pushes the water out when the spigots are opened.