We decided to do a medium size rain water harvesting project by collecting water off the roof of our outbuilding shop/garage/barn. The idea is that this manageable size system could provide water for the garden and some trees, and that we could learn from it and decide if we want to do a somewhat larger system using the house roof which provides quite a bit more collection area.
The shop building with its gambrel roof and the extension shed roof on one side provides a total of 925 sqft of equivalent flat collection area.
We added gutters to the east and west sides to pick up the water, and then ran PVC piping to a 2500 gallon plastic tank located under the south end of the lean-to roof. If the 2500 gallons seems like quite a bit of capacity, it initially seemed that way to us, but even in our not very high rainfall area a thousand square foot of roof can harvest a respectable amount of water.
The water collected by the gutters goes to an inlet at the top of the tank. The plumbing has provisions for diverting the first few gallons of each rainfall to eliminate some of the dust etc. that accumulates between rainfalls. Water is removed from the tank via a fitting near the bottom and pumped to the area needed with a 120VAC pump. There is an overflow pipe that connects to the tank up high to run water off to some useful location when the tank fills up and overflows.
The sections listed below give quite a bit of detail on the sizing and construction, which is all pretty simple. There is a comments section on the last page to ask questions and offer advice.
Collection (gutters and piping to tank inlet)
Delivery (plumbing and pumps to deliver water to garden)
Overflow (system to manage overflow)
Comments (questions, improvements, corrections...)
Gary July 3, 2011