News Editorials Water Themes Water Supply Myanmar Water Portal Monday, 03 October 2022
What is a Rainwater Harvesting System?
Rainwater harvesting is the collection and storage of rain for reuse on-site, rather than allowing it to run off. These stored waters are used for various purposes, such as domestic use, gardening, irrigation, groundwater recharge and flood retention, etc. If filtered, rainwater can also be used as drinking water. The two main benefits of a RWH system are:
- Use of the collected rainwater (drinking water, domestic use; change in relation to the situation)
- Decreases risk of flooding – collected rainwater does not enter the drainage system and thus releases pressure on the drains. However, the overflow needs to be properly directed (either to an infiltration area or into the drainage system).
How to build a Rainwater Harvesting System
Among many kinds of rainwater harvesting methods, Rooftop Rainwater Harvesting is the most suitable method for domestic use. To build a Rooftop Rainwater Harvesting System, suitable roofing material is necessary for roofs that are used to collect rainwater. Roofs made of toxic materials like lead and copper should be avoided. Fortunately, most Myanmar households’ roofs are using galvanised iron sheets as roofing material which is suitable for rainwater harvesting. But if there are any rusts or holes in the roofs, they need to be repaired or replaced. Moreover, before the rainy season, it is necessary to clean out rubbish, animals’ faeces and fallen leaves from the rooftops so that harvested rainwater will be less contaminated and the cost of water treatment can be reduced as well.
Components of a household rainwater harvesting system and their functions;
- Mesh filter: to filter out leaves and rubbish before rainwater flows into gutters
- Gutters: to be installed around the roof to collect rainwater from all around the roof.
- Downspout: a pipe to connect the gutters to the rainwater storage tank.
- Fast Flash Diverter (valve & pipe): to divert rainwater from the downpipe during the very first rain and let it flow into a drain or infiltrate into the soil, instead of into the storage tank. As the roof can still have some dirt and debris, it is needed to prevent this from entering the storage tank directly.
- Cloth filter: to filter out small sand-like particles and to prevent insects from entering and it is installed at the junction of the downpipe and storage tank. But it can slow down the water flowing rate into the tank. So, if you already have a separate drinking water filter at home, there is no need to place the cloth filter at that junction.
- Water storage tank: to collect and store rainwater. Even though the larger the tank size, the better for the water storage, it may also change depending on the available space in your yard, and the rainfall intensity in your area. In our pilot project, we used the most suitable size of 2,000-litre water tanks after detailed calculations.
- Spigot: to get water out of the tank for the consumers. It should be at least 10 mm above the bottom to prevent sediment from being in the water that will be used.
- Excess Water Diversion Pipe: to spill water from the tank to the drain or into the soil when it overflows. At the junction of the tank and diversion pipe, a cloth filter should be installed to filter out bacteria entering from outside.
- Water Level Measuring Ruler: to indicate the amount of water in the tank to know how much water gets in and how much can still be used.
- Water Meter: to show how much water has been already used.
- Raised platform (optional): to be installed at some height, to make it easier to take water from a tap.
Additionally, you can connect your rainwater harvesting system to other storage tanks or to other users if you wish to. By following these steps, you will be able to install your own Rainwater Harvesting System with relative ease.
Operation & Maintenance
It is necessary to know and remember the following key things in the operation of the Rainwater Harvesting System.
Step 1: Check and repair your roof as needed to prevent any holes or leakages.Step 2: Clear any trash, leaves, or other debris from roofs, gutters, pipes, drains, or any other parts of the system as much as you can.Step 3: Clean the inside of your tank, especially at the bottom where there may be sediments. It is recommended to clean it once a year, before the start of the monsoon season.Step 4: Turn the valve of the First Rain/Roof Cleaning Separator component of the system at the beginning of the rainy season and when cleaning the gutter to divert water away from the tank. This allows dirty water to flow away from the tank to prevent your tank from being contaminated. After a long period of summer, the roof tends to be unclean with dust or other debris, so be sure to do this until the rain has washed away the dirt from the roof and the water coming down is clear.Step 5: Once the water coming from the roofs and gutters are clear, turn the valve again to divert water to the tank so it can be collected.Step 6: Turn on the faucet to use the water in the tank. Excess water will come out from the overflow outlet of the tank by itself during heavy and long rain – you can choose to connect this to another storage tank, or an infiltration area if you wish.
1. Should the storage tank be circular or rectangular?
Using circular or rectangular tanks does not matter, but the location might influence which shape of the tank can use the space the most efficiently.
2. A high or low tank? What size should it be?In general, the tank should be as large as possible. Therefore a high tank is better than a low tank but it should not be higher than the lowest point of the roof, as the volume of the tank will never be filled, which is a bit of a waste of money. 3. Is it okay to place the tank on the ground directly?Indeed it might be needed to compact the soil to make a good foundation for the tank. Try to prevent using concrete as much as possible as this prevents infiltration. On the other hand, you can also put your tank on a raised platform which is to be installed at some height, to make it easier to take water from a tap.
4. Is RWH only feasible for new buildings?No, indeed existing buildings can also implement RWH by modifying the existing plumbing and making additions, if necessary.
Source: Yangon Htee City Project