Formalised Water Collection
RainWater Cambodia has identified measures to combat the risks in traditional rainwater harvesting and has developed a formalised, risk management approach to rain water harvesting. A typical design of our rainwater harvesting systems considers the following elements:
- Monthly rainfall data
- Available harvesting area
- Harvesting area runoff coefficient – this takes into account losses from the roof/catchment system and gives an estimate of the actual amonut of water that can be expected to be collected from the roof
- Usage/demand per user
The systems can be sized based on supply, demand and budget.
Typically a graph plotting cumulative rainfall against cumulative demand will determine if the supply will meet the demand. From this type of graph the maximum storage that would be required can also be determined. This is particularly significant in areas where there is a monsoonal or single wet season, such is the case in Cambodia.
There are 4 key elements to a rain water harvesting system:
- The bigger the harvesting area, the more water can be collected during any rainfall period.
- The smoother the harvesting area, the greater the % of water that can be collected.
- Metal roofs may provide some additional benefit if subject to the hot sun as this may contribute to bacterial die-off.
Conveyance system – guttering and pipes:
- This part of the system helps to maximise the quantity of water that flows to the storage tank.
- The conveyance system can be enhanced to maximise the quality by adding leaf guards and first flush diverters.
- Most emphasis is usually placed on this component as it is generally the most expensive part.
- The storage capacity needs to be adequate enough to enable water to be stored to last through the dry period.
Risk management components:
See detailed comments in the next section.