First flush diversion is a good idea to avoid capturing the first bit of a rain to wash the dust and dead squirrels off the roof. 10 gallons per 1000 square feet is a good rule of thumb. There are fancy gadgets for that, but a standpipe with a valve at the bottom seems to be the one that works. It ties into the gutter right before the downspout, so it has to fill before water can flow past it to the downspout.
A 6″ pipe holds about 1 gallon per foot. An 8″ pipe holds about 2 gallons. How can we make it look good?
Tags: rainwater harvesting
How is the valve supposed to work?
The simple version would be a 3/4″ hose bibb at the bottom. After a rain you manually open it and let the standpipe drain.
I’ve also seen a metering valve at the bottom so it drains slowly without any human intervention. Or I think you could just leave the 3/4″ hose bibb cracked open a little all the time. There needs to be a cleanout right at the valve to fish out the leaves and dead squirrels if the drain gets clogged.
The Texas Rainwater Harvesting Manual has more info on PDF page 13 and 14.
I’m wondering if using a roof washer like the one in the Tmanual (PDF page 15) isn’t a better more general solution because it doesn’t require maintenance after every rain. It also seems like it would be easier to deal with aesthetically because it can be set in the ground.