Intermediate rain harvesting system - non potable and pressurized pump with backup water system

This system is more complex than the basic system and has a pressurized pump and control system together with a municipal backup water system.

This example will harvest water off a 250sqm roof. Water is non potable and can be used for washing, gardening and be connected to toilets and washing machines. It also contains a switch-over backup system if the municipal supply is interrupted or if the rainwater tanks are empty.

Key components:

  1. Three round 5000l interconnected rainwater tanks. (15000l tank storage is the minimum in this application) An ideal would be 20000l tank storage capacity.

  2. Gutter and down-pipe modification in order to ensure that all the harvested rain water is directed to the interconnected rainwater tanks.

  3. Good solid hard surface/platform for tanks and pump

  4. Redirection and changes to gutter down pipes.

  5. Two inline primary WISY rainwater filters or one WFF 100 vortex filter (for this example we will use the WFF 100 vortex filter). All the water from the gutters will be directed to a single 110mm pipe that interconnect with the WFF100 vortex filter.  The primary vortex filter is self-cleaning and screens  out any organic material greater than 280 microns. It ensures that the rainwater tank is kept clean with minimal sludge buildup in the tank, thus improving the water quality and reducing the cleaning frequency of the tank (you would only have to clean the tank once every 5 years).

  6. One multi siphon overflow with vermin and insect protection. You want to protect the water quality in your tank. The multi siphon overflow prevent any insect or vermin from getting into the rainwater tanks - especially where the overflow is connected directly to the underground storm-water pipe.

  7. One calming inlet that will allow fresh rainwater from the vortex filter to enter the bottom of the tank and not disturb the sediment and microbiological layer on the bottom of the tank

  8. Tank level gauge so you can see the water level in the tank

  9. One floating suction connected to the suction of the pump. The floating suction draws water from just under the water surface ensuring that the old water in the tank is used first - keeping water fresh at all times in the tank.

  10. One externally pressure pump with a pressure controller  mounted on on a pressure tank. We have found that this is the most cost and energy effective system as it does not start the pump when small amounts of water is used. It is fully automatic and as soon as a tap is opened fully,  the pump will start to provide flow  and pressure. You can also use a submersible pump, but for this example we will use an external pump.

  11. One fine screen filter on the pressure side of the pump to ensure that there are no particles in the water that can damage sensitive plumbing equipment.

  12. Once municipal top up solenoid valve and float switch  system. By setting the a minimum water level in the tanks an electrical solenoid valve will always top an minimum amount of water to the tank.  Thus if there is no rainwater or if the tanks are starting to empty,  the system will automatically add some water to ensure you always have water for flushing toilets and washing. When it rains and the tanks fill up it will stop and the system will only use rainwater.

  13. One municipal switch-over system and bypass valve system. If anything goes wrong or if the system need to be maintained you can bypass it and simply use municipal water for a while.

  14. Backflow preventer valve and assembly. This is a critical element of the installation. When there is a risk that you can pump any water, but municipal water back into the municipal supply, you have to install a backflow preventer. It is not a non return valve, but a specialized valve built and designed for these applications. It also has to be inspected  by a specialist plumber every year

 

Positive aspects.

  • The building is harvesting and using rainwater more effectively

  • If the municipal supply is interrupted the building will still have pressurized water to flush toilets.

  • This system work well in small industrial applications like supplying make-up water to cooling towers.

  • A good trained plumber with experience and the right components can do this type of installation.

  • Installation time is about 4-5 days.  

  • For a few thousand rand extra you can easily convert this system to a fully potable rainwater harvesting system.

 

Negative aspects

  • The water cannot be used for potable applications or in baths or showers, as it has not been treated and there might be a small risk of contamination.  Therefore you are not fully utilizing the opportunity to use the harvested rainwater. There might be period during the summer rainfall season where the rainwater tanks will overflow because the rainwater in the tanks are just not used fast enough. Our estimate and simulation shows  that you will lose approximately 25% of the potential harvested water in this way.

  • The building requires a dual plumbing system to the bathrooms - rainwater to the toilets and municipal water to the tap and basin - which can be costly.

 

Costs - Installed on site (Please note that these are estimates and can be used as guidelines only)

 

  • Three 5000l interconnected  tanks - R19000
  • One Wisy WFF100 vortex filter  R7000
  • One multi siphon overflow R2600
  • One floating suction R1000
  • PVC Down-pipe and fitting  R2000
  • Tank Base with R4000
  • Tank Gauge - R500
  • Pressurized pump with pressure tank and controller R5500
  • One pump cover R800
  • One Solenoid make-up valve system with level switch R3500
  • One Municipal switch-over system R1000
  • One Backflow preventer assembly R2100
  • Valve, brackets,  and accessories R3000
  • Design, Installation and commissioning -  R15 000

Total R 65000

 

Potential amount of rainwater that can be recovered in a coastal zone with 1040 mm of rain per year is 185 000 liters per year.

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