Rainwater Harvesting (Part 2)

by longtallyarn

The Great Pour

We decided to buy ready mixed concrete from the professionals and I called “Ready Mix Concrete” and conveniently arranged to have the concrete poured.  This was the only thing so far that had been fast and easy.  It wasn’t cheap but it wasn’t much more than it would have been to buy that much quickcrete.  I arrived home from work an hour early and the twins were set up to watch Sesame St. on the laptop.  We had to answer some questions about whether we had a septic tank that could be crushed by the truck before the driver would bring it through the yard.  The concrete poured in minutes.  Then we smoothed it out as best we could, had the driver make some stepping stones with the extra, and let him leave.  The boys liked seeing the big truck in the yard and agreed to come out and put their handprints on the foundation.

The Cistern and Plumbing

After the concrete dried, we brought home our tank. Oso went to U-Haul to rent the trailer (and, long story short, also came home with a part time job) and then went to Agrisupply to purchase the tank. Our friend, Anna, was helpful enough to go along in an advisory capacity and then helped us with the unload.

We decided to paint the tank to discourage algal growth.  We rolled the tank around the yard until we had completely painted it black and then white to exclude light.  We used water based paint because we didn’t want something that would interact with the plastic of the tank but it tends to peel off easily with any abrasion.  Maybe oil based would have been better.

When my parents visited they helped us set the tank on its foundation.

After much indecision we purchased PVC pipe and some screen filters.  The Rainhead brand screen filter is installed under the downspout, before the water enters the pipe that leads to the tank. These screens do a good job of diverting leaves and twigs.

We also constructed a first flush diverter, a vertical pipe with an end cap that should capture solids, such as dirt or bird poop that may wash off the roof at the beginning of a rain fall event. The idea is that the first few gallons of water that hit the roof go into this system and stay there until someone empties it later. Subsequent water is cleaner. A first flush diverter should provide about 10 gallons of storage for every 1000ft2 of roof.  We have a 5 gallon diverter for the back of the house and will add a 2.5 gallon diverter for the front left side later if we tie that in.

We want to make the water tank area of the yard more visually appealing and fruitful and we plan to construct a trellis for growing some kiwi vines. To this end we embedded three 4x4s into the concrete to support the trellis. If we had realized how heavy the first flush diverter would be when filled with water (about 45 lbs) we would have added a fourth post to this set up to support it. We didn’t want to screw the pvc system onto the siding so Oso later dug 5 feet down into the ground on the back corner of our concrete foundation and installed a very long 6×6 that will support it.

(We still need to install the little tap on the end of the diverter so we can empty the water in an civilized manner instead of the gooey kablooey that results when you remove the endcap in one smooth motion.  No matter how slowly or quickly you pull it off the end of the pipe 5 gallons of water will splash all over you–not too bad in the summer but in the winter it is cold and messy.)

Finally, the opening on top of our tank is covered in a strainer basket in the 18-inch opening where the lid would go if it were closed. This should keep out anything that makes it past the other systems and keep mosquitoes and vermin out of our water.

Future Considerations

Since we didn’t seal the top of the tank we don’t think we will need to put in an overflow pipe. Water can just flow out the same opening it flows in, although we hope to prevent this by doing this by using or discharging the water during dry weather.

Our roof is about 1000 square feet with 4 downspouts. The original plan was to eventually route three of the downspouts to the rain catchment but first we connected only the closest one, the rear left. In future projects, we may change the tilt of the guttering on the back of the house to include water from the rear right downspout and construct guttering from the front left corner.

In the first month and a half, our 1500 gallon cistern filled to the brim. Now that it is cold our garden doesn’t need much water. We are using the water around the yard as much as possible but we regularly need to bleed some out onto the backyard when we have a sting of dry days.

In the summer we do not expect to do this because of the needs of the garden. We would like to be able to use this water for doing laundry but even though our town is running out of reservoir our sewer authority doesn’t authorize this because we would be disposing to sewer water that has not been billed for sewer.

We still need practice at regulating the level of the tank. I have realized that the winter rains we get tend to be sustained, heavy rainfall events, so I need to maintain the water level and maybe 500 gallons instead of 1000 so that we can accommodate 3 or more inches of rainfall at once.

Did it work?

Well, it depends on your perspective.  We are collecting enough water to do any water related chore around the garden we can think of.  This is sustainable and good for emergency preparedness.  Check.

We did not completely stop the entry of water into the basement.  Maybe we were hasty in choosing our damp basement solution.  I still think the cistern helps, especially from the angle of stopping seepage.  However, the real floods happen when the yard becomes waterlogged and the combination french drain/basement floor drain backs up with water.  Cleaning this out is a project for this spring, we hope. We are also piling up some soil around the outer walls, which, theoretically will cause water to run away from the house instead of toward it.

In Conclusion

We learned a lot and got a lot of experience with planning and doing construction projects. We have water to use and enough to waste without feeling guilty. Oso and I had a good time working together on it and we are proud of ourselves for installing this large feature in our backyard.

The Long Tall Yarn inscribes the date.

The Long Tall Yarn inscribes the date.

The Big Day.

The Big Day.

What it looks like now.

What it looks like now.