The Rainwater Treatment Train
You have been through the previous blogs and have now decided that you want to investigate the feasibility of going the next step and installing a system to provide your entire household with rainwater.
For this you will need to follow the guidelines as discussed in the previous Blog:
- Leaf screen/eater
- First flush diverter
- Tanks that have coating or similar to prevent light transmission
- Any of the bulk storage tanks that have gutter inlets need to have a bottom drain to flush coagulated/settled matter
- A pump outlet about 300mm or so above the drain level.
We recommend that all tanks that have gutter water feeding into them, have a bottom drain as above.
What Next?
Now you have the bulk water storage and connection for the pump, we can discuss the rest of the treatment train.
A small pump is installed to pump the water from the main storage to the dedicated clean water supply tank and push the water through the filtration train.
Filtration Train
- 3/4’” or 1” Arkal or similar 100-micron disc filter. These filter discs will remove the majority of the particulate matter and as they are washable it will reduce the number of filter cartridges you will use over time.
- 3 stage big blue filter with the following filters
- 10 micron Polyspun or similar filter cartridge
- Refillable cartridge with Silliphos. This will help protect all metal surfaces and piping from scaling or corrosion
- Carbon Bloc Filter. This filter helps remove any tastes, odours, pesticides, herbicides and volatile organic compounds
- A 10×54 Frp vessel with calcite media, this will address the acidic nature of our rainwater and increase the pH and alkalinity of the water. This filter has a bypass across it, so that you can bypass a portion of the water should the calcium level increase too much
- From here the water enters the dedicated clean-water storage tank
- An in-tank U.V. sterilizer is installed in this tank to sterilize the water and keep the tank environment sanitized
- From this tank a booster pump is installed to supply the household with pressurized water on demand. Currently we use variable speed constant pressure booster pumps, due to their constant pressure, energy efficiency and the fact that there is no in-rush current, so they are compatible with solar systems
Further Recommendations
We recommend that the storage tanks be treated with peroxide regularly, once every two weeks or so, to keep the storage sanitized and prevent the build-up of bacteria etc. in the water and filter system. We also recommend additional treatment if it rains after an extended dry spell as this is when the water from the roof ientering the tanks is at its most contaminated. We do not recommend using chlorine for this as the water from the roof will contain elevated organic carbon and when chlorine is used with this it will create unwanted, carcinogenic by-products.
Final Thoughts
It must be noted that South African Law is very strict on the quality of water distributed and the onus is on the owner of a system like this to ensure that the water fulfills the requirements of S.A.N.S.2421 for domestic water. Should you supply water, and someone becomes ill and it is traced back to the water, liability could be a problem.
Our general feeling is that the risk involved with supplying a full domestic solution from rainwater is not worth the risk, unless you have no alternative, or it is a short term “drought or similar event. Our feeling is, it is safer to use this for all non-potable applications, and use municipal water for baths, showers and kitchens, and rainwater for washing machines, dishwashers, pool filling and irrigation.
