In my last post I talked about the catchment and conveyance portions of my team’s rainwater harvesting design in Grand Ravine. Now I will explain the final portion of our design: storage.
The tank is the most important part of the storage model. An above ground tank is preferred for smaller scale harvesting due to the fact that it is more accessible and easier to maintain. There are a number of shapes and structures that the storage tank can take, but the most fitting one for the Grand Ravine area is the Thai jar model. It is suitable for small pathways, it is inexpensive, and relatively easy to make. This rounded tapering tank holds up incredibly well under the pushing forces of water because the stresses are well distributed throughout the tank. The smaller size makes it the best option for incremental widespread adoption of the rainwater harvesting program as it is easy to use modularly. With the Thai jar tank, each household could become self sustaining in a few years. Additionally, the tanks are cheaper, easier to mass produce, and require less upkeep and sanitation due to the fact that they will be filled and emptied more often. This yields a very high material usage to capacity ratio.
The material being used to make the tank is a combination of ferrocement and stabilized soil. Ferrocement is a mixture of regular and waterproof cement that is reinforced with some sort of wire to make the cement more flexible. After evaluation, square mesh wire seems to be the better reinforcement option over chicken wire because it has a higher volume fraction so it is more durable. Stabilized soil is a combination of cement and sand that serves the same purpose as an entirely cement tank, but is cheaper and more accessible due to the fact that soil and sand are both readily available in the Grand Ravine.
The tank should also have a top on it to keep debris out. Having a top makes maintenance, refurbishment, and cleaning easier. The storage facility should also contain a tap for water retrieval, and a brick stand so that the tank stays above ground. The tap should be located a few inches from the bottom of the tank to allow a certain amount of water in which debris can settle for further filtration.
Lastly, the tank should have an overflow pipe attached to it to prevent the system from becoming overwhelmed by excess water. Though not a part of the design being discussed in this report, having multiple central storage centers whose water source comes from households’ overflow pipes could be considered. This already filtered water could be run through pipes to a few locations throughout Grand Ravine and be sold to people who need more water than their personal harvesting systems are able to provide. The water could be chemically treated and managed by the government as another source of potable water.
Though this system was created within the context of a developing country, you can apply the rainwater harvesting technique to your own home to reduce water used and help make a positive environmental impact. I hope you found this interesting!