Peter Campbell's rainwater harvesting project. (Last updated December 15, 2010)
The covered walk between the back door and Garage has gutters that drain on either side of the back door. There aren't even any downspouts, just a hole with a small "lip" to kind of direct the falling water away from the walkway.
This always seemed like bad design to me but it also was a perfect place to start collecting rainwater. We sometimes set a bucket under the gutter but it became a mosquito hatchery and didn't hold much water, so I decided to get a real water tank. Right next to the back door was OK for a bucket but no so good for a large water tank, so I decided to put it at the other end of the walk, next to the garage. This required relocating the gutter drains. Luckily the gutter was perfectly level, not sloping toward the back door. So all I had to do was plug up the old holes and make two new ones at the other end.
The ground slopes up toward the garage, with so I needed to make a level pad for the water tank. The advantage is this makes the tank higher and gives a little more water pressure.
It was easier than I expected to set some concrete blocks on the lower side and back fill with decomposed granite. The resulting pad is almost as stable as concrete and much cheaper!
I got a great deal on this 300 gallon water tank at tanksforless.com. I also got a Leaf Eater from them to keep debris washed out of the gutter from entering the tank. You can see it just below the gutter. It also keeps mosquitoes out of the tank. At first I was worried the tank might be too tall to fit below the gutter and would be unstable, but when I set it in place it fit the spot perfectly and the decomposed granite pad is extremely stable. It shows no tendency to tip or sink into the pad at all, even when full to the top. 300 gallons of water weighs about 2,500 pounds! That height is another water pressure maker, and when it is full there is plenty of pressure to get a good flow through a hose, although not enough for a sprinkler!
I made a first flush diverter with a 5 foot length of 3 inch pipe below the leaf eater. The first two gallons of water from the gutter fills that up to the tee and then the rest of the (hopefully cleaner) water flows into the tank through a 1 1/2 in pipe connected to the 1 1/2 inch fitting at the top of the tank. The gutters drain only the small walkway roof, less than 200 square feet I estimate, so that pipe should be large enough. The pipe is connected to the tank and the leaf eater with flexible couplings at each end since the tank could shift a little as it fills and empties. I put a cheap PVC spigot in the 2 inch fitting at the bottom of the tank using a couple bushings to get from 2 inches down to 1/2 inch.
A couple days later we had about a half inch of rain. I made a sight gauge from some clear tubing and a hose fitting with a red golf tee as a float. It showed I got about 50 gallons of water from a half inch of rain, so it would take about 3 inches of rain to fill it. Since we can get more than 3 inches in one good storm, I though I better arrange an overflow.
The overflow is simply another 1 1/2 inch pipe connected to the fill line with a tee and elbow, with a short pipe from the tee sloping up and the drain sloping down from the elbow. Water has to fill the incoming pipe completely to spill over the hump at the elbow, and after that all water will go onto to the driveway on the other side of the fence. To keep mosquitoes from entering the tank this way, I cut a 1 1/2 inch round piece of window screen, put it in the tee socket and sandwiched it in with the end of the pipe pressed into the tee. I didn't glue that connection so I can replace the screen if needed. Since this is just an overflow, a little water leaking at the joint shouldn't be a problem.
Now that I have a good overflow, I want more water!
The picture above shows the main house and gutter. You can just see a downspout at the corner. In the pictures below you can see how I redirected that downspout to empty onto the roof covering the walk. I estimate that should quadruple the amount of water captured. If that overwhelms the 1 1/2 inch fill pipe I'll have to undo that change.
A view from the driveway.
We haven't had any rain since that change, so we will see!
The latest addition is a 2 inch ball valve before the spigot at the bottom of the tank. This will allow me to change that spigot out or connect extra pipe there without draining the tank. And the valve is a full 2 inches to match the bulkhead fitting in the tank. I might want to have several pipes connected here later and don't want to restrict the flow at all by using a smaller valve here.
A few weeks later I tested the flow rate of the cheap spigot against a nice 3/4 inch ball valve. The difference was DRAMATIC! The 3/4 inch ball valve has a much higher flow rate, especially with the tank very low on water, so that is now what I am using. I also put in a tee to connect a 3/4 inch pipe that runs under the back sidewalk and along the side of the house to the front yard. The 2 inch ball valve did make it easy to change these valves with water in the tank, but the combination with the tee and other valve just stuck out too far from the tank, so I removed the 2 inch valve.
I made a plug from an old tennis ball and some pipe and wood scraps. The handle in about 8 feet long so I can reach the 2 inch outlet at the bottom of the tank from inside from the manway at the top of the tank and plug it to work on the pipe. The obviates the need for the 2 inch valve.
A view from the driveway along the side of the house. You can see the slope and barely see the other valve at the front corner of the house, past the gas meter.
You can see how much lower the front is from where the brick starts. The rest of the front yard slopes down maybe a foot more to the street. That down spout drains the front part of the roof. I might connect it to the pipe and get more water to the tank, but I would need a bigger tank to justify doing that.
