Critical design elements for a rainwater harvesting  system

If you want to design and build a rainwater harvesting system that will deliver optimum water recovery and add value to the property you must follow the guidelines set out below:

  1. Size your rainwater storage tank correctly 

    • In order to understand how much rainwater can be captured you need to know the surface area of the building or structure that will be used to capture the rainwater. By using the average annual  rainfall data in your area you can calculate how much water will be captured during an average rain season.
    • This will give you an indication of how much water you can capture and how big your storage tank should be. The storage tank is one of the more expensive components to a system. We have found many systems that have too little storage capacity and lose a lot of potential water.
    • Don't size it too big because you want it to overflow every once in a while to flush of a bit of the surface layer of water.
  2. Analysis and understanding of flow and pressure requirements
    • It is critical that the installer of the system size the correct supply pump for the application. This can only be done by doing a flow analysis and water volume requirement for the household or business. We find many installations where the wrong booster pumps were installed – resulting in over-pressure and damage to household equipment or low pressure and low water flow to the house. 
    • Piping need to be sized correctly for the flow requirements. Too small pipes will result in pressure loss in the system
  3. Understanding water quality and ensuring it is treated correctly
    • Water pH and quality vary and it can have a significant impact on your water pipes and appliance. The risk is slow and costly damage and corrosion in the long term. By analyzing the water quality and installing the correct treatment equipment you can extend the life and  prevent damage to your appliance and piping systems.
  4. Managing and effective control of organic material in your water storage system
    • We have proved that effective pre-fitration before rainwater goes into the rainwater tank is the biggest critical success factor for consistent good quality rainwater
    • Big pieces of organic material (leaves etc) can adversely affect the quality of water in your storage system. It is critical that pre-filtration prevent an increase in the organic load in the storage tanks,  and this must be incorporated in the design. It should be a system that is easy to maintain at a very low cost.
  5. Ensuring an effective and undisturbed bio layer in the storage tank.
    • The controlled amount of organic material in the storage system settles to the bottom and acts as a natural filtration and cleaning system in your storage tank. The design should ensure that the bio layer is not disturbed and that there is sufficient oxygen in the water for it to function optimally.
  6. Effective filtration systems
    • It is important that the filtration system is correctly sized for the application and the sanitizing system. Incorrectly sized components can lead to ineffective filtration and the risk that the water is not properly sanitized which can result in bacteria and unwelcome pathogens ending up in your water supply.
  7. Backflow prevention of treated water into the municipal system
    • There is always a risk that treated water can find its way back into the municipal water supply system. In order to prevent it from happening it is imperative that a backflow prevention valve is installed. This is a legal requirement in many countries and just good engineering design practice when installing a system.

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