Rainwater Harvesting Project (Part 1, Summer 2014)

by longtallyarn

When we bought our house we knew that heavy rains sometimes infiltrated the basement so we decided to install a cistern. We reasoned that capturing most of the water that falls onto the roof and preventing it from going down the gutter into the soil beside the house it would help to keep the basement dry. Also, we wanted the water for our garden. It seemed an exercise in sustainability and emergency preparedness—appealing to both my spouse and I. Saving money on utilities was never a motivator because the cost of tap water, even long term, is not comparable to the set-up cost of a large cistern.

We started the project in the last week of May 2014 because I wanted it finished in June to catch some of the June rains we usually get. Ha! The project stretched out until early September and consumed WAY more time and about twice as much money as we had anticipated.

Personal Considerations

  1. Our children are 2 years old (now going on 3) and are not inclined to sit idly by and watch other people dig in the dirt, spray the water hose, mix cement, etc. so Oso and I were limited in the time we could work together on the project.
  2. I work full time outside the home, and Oso works full time inside the home, see item 1.
  3. We had to watch our budget carefully.
  4. We had to research each step of the process and this took time. Between internet resources and several books we borrowed we were able to piece together our plan but we never found a great resource that delivered all the information we needed.
  5. Oso was learning how to work with brick, block, concrete, and PVC on the job. I think he did great!

Technical Considerations 

The Tank

 A rainwater collection system produces approximately 600 gallons from a 1000ft2 surface for every inch of rainfall.  Since our main motivation was stopping the water infiltrating the basement it was difficult to determine the needed tank capacity. Most resources are written for people who need a household water supply. They decide how much water they want to use during the each month, determine the length of the driest season they have on average, and then size the tank to get them through it. I decided to look at the wettest month we have, March, and size the tank to hold all the average rainfall that will land on the applicable parts of our roof during that time. Maybe that seems random but I had to start somewhere. We were only planning to collect from ¾ of our roof so 1500 gallons seemed appropriate. When we began telling our friends and family about our plans several of them recoiled in shock. I doubted myself and thought about reducing the volume but in the end we decided to go with 1500 gallons.

 The tank is 10 ft. tall and 6 ft. wide. We selected the “vertical” tank, tall and thin instead of short and squatty, because this would save money on the size of the foundation. We thought it would look more attractive beside the house, and maybe give us slightly more water pressure. It’s a little less convenient because we can’t look into it or clean the filters without a ladder. The occasional climbing makes it more dangerous from a maintenance perspective but it might be safer overall because persons can’t fall into it without climbing up there first.

The Foundation

Another complication was the fact that the only hill in our yard is on the spot where the tank should sit. Normally a large water tank can sit on a sand bed but because of the hill we went with a concrete pad. Oso asked Facebook and consulted some websites about the depth of foundation needed to support a tank that could weigh as much as 12,500 lb. We decided to dig down to a depth that would put us at 2 ft on the downhill side and about 3 ft on the uphill side. This depth also insured that we weren’t building our house on the sand, so to speak, and digging slowed considerably as we dug well into the clay subsoil.

We decided to pour a square of concrete that would sit on the clay and support our water tower. We would make a cinder block frame  that would stay in place. We realized as we were digging that it was going to be difficult to get the dirt as level as it would need to be to accommodate our cinder block frame.

We were under the impression that if we mixed up about 8 or 10 bags of quickcrete and poured them into the footer it would self-level. Since we were not that experienced with the substance we were surprised to find that quickcrete is filled with rocks and did not smooth itself out well at all. We had to try to level it with a hoe, and also we probably added too much water. The surface of the quickcrete was a little powdery after drying.

We brought home a bunch of blocks and some mortar (the blocks were cheap, the mortar was not) and we began the process of mixing mortar and laying blocks. I was the assistant who cleaned up the tools, measured the water, and handed things to the block layer, although Oso sometimes wondered aloud if I was assisting him or he was assisting me.

We didn’t want the edge of the hill to be taller than our block frame so we placed a layer of bricks on top of the cinder blocks to make it a little higher and also to add a decorative edge. Our side porch has the same decorative edge on it, although maybe a little more precisely rendered. It took us a long time to place all the bricks and blocks because we worked slowly and therefore had to mix up very small batches of mortar. Some days we only placed 4 or 5 blocks during the window we felt comfortable leaving the kids in front of Sesame St.

Finally we were ready to call “Ready Mix Concrete” for some ready mixed concrete.  Tune in later for Part 2. 


Here is Oso digging the trench that would become the footer.



Here is Oso with the footer in place. His outfit, same as above, would suggest that this work was all accomplished during the same day. Or it might suggest that it took so long that he cycled all his work clothes through the laundry and eventually arrived at this outfit again. 



Here is Oso placing the second row of block, this time wearing home-made tie-dye.



This photo shows the placement of the supports for our future vine trellis. We embedded them into the concrete pad. Oso leveled them from two directions. He obsessed about this a little while we were waiting for the concrete truck to arrive, going out each day and moving them a bit until he felt they were as straight as they could be.  When I first met Oso he only wore black shirts.  I have added color to his life.  See above.



Waiting for Ready Mix Concrete.  This is the rebar grid that Oso constructed to add tensile or ductile (or whatever) strength to our concrete pad. I wanted to throw a bunch of rusty old metal in there at random, as I have observed other people sometimes do, but Oso wanted to do it right. And we didn’t have that much rusty old metal laying around the yard anyway.