Rain Water Harvesting System

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Water conservation is a crucial process in creating a sustainable world. This has led to the introduction and integration of Rain Water Harvesting (RWH) systems in Malaysia.


Figure 1: Rain Water Harvesting Tank typical installation [1].

Surface tanks are frequently provided on residential, commercial or industrial lots for rainwater harvesting systems. These tanks collect rainwater from the rooftop of the building, filter it and then store it for intended domestic use as shown in Figure 1.


What Are The Requirements by SPAN?


Suruhanjaya Perkhidmatan Air Negara (SPAN) has put forth a guideline that must be adhered to. Section C.5.2 Use of Non-Potable Water of the Uniform Technical Guidelines Water Reticulation And Plumbing [2] states the following:


C.5.2 Use of Non-Potable Water


a. Rain water harvesting system, if adopted by the consumer, shall be tailored to supply water for:-
       i. General washing and gardening.
      ii. Flushing water closets.
b. There shall be no cross connection between non-potable and potable water distribution systems within buildings.
c. Distribution pipes for supplying non-potable water shall be painted green along its entire barrel.
d. Taps and outlets for non-potable water shall be clearly identified as ‘Not for Drinking Purposes’.
e. The water storage cistern for potable and non-potable water shall be separated and shall not be inter-connected.
f. Any service pipe conveying potable water to top-up a rain water storage cistern containing non-potable water shall have a backflow preventer of the Dual Check Valve type; and the service pipe shall terminate at least 225 mm above the overflow level of the rain water storage cistern.


A few highlights from the above excerpt include, RWH water shall not be used for human consumption. RWH water shall only be used for washing and gardening. There shall also be a conspicuous sign at each RWH garden tap that clearly states, “Not for Drinking Purposes”. This sign shall be written in both English and Bahasa Malaysia.


Should RWH Tanks Be Used To Supply To WC Cisterns?


Should the rainwater harvesting tank supply water for domestic washing or to WC cisterns? A study was conducted by Taylor et al. (2020) [3] to determine the risk of Legionella transmission from rainwater harvesting (RWH)-fed water toilet flushing.


The findings determined that Legionella spp. presence was successfully isolated from three of the four RWH tanks. Legionella could be dispersed via aerosols from a toilet flushed with water from a RWH system and the effect would be more pronounced in smaller, enclosed areas. The researchers concluded that the amounts are negligible and are unlikely to pose a risk to human health.


However, the risks are unknown especially from older RWH systems that are not frequently maintained. It is our belief that RWH systems should not be used for WC cisterns even though it is entirely permitted by SPAN to do so. On top of that, it is best not to use rainwater to fill the WC because of the high acidity of the rainwater, especially in urban areas. This causes yellow staining on the WC bowl reducing the product lifespan and may pose a threat to health.


Our M&E Consultant Solutions


As M&E consultants, our solutions for Rain Water Harvesting includes:

  • RWH system design
  • RWH schematic design
  • RWH tank sizing calculation


Perunding JW is an M&E Consulting firm based in Malaysia. If you are looking for more information or resources, reach out to our team of engineers. We will gladly assist you. Visit our homepage or call us at +603 7955 5918.



[1] Department of Irrigation and Drainage, “Rainwater Harvesting Guidebook,” Rainwater Harvesting Guidebook, 14-Aug-2017. [Online]. Available: https://www.water.gov.my/index.php/pages/view/585. [Accessed: 13-May-2022].

[2] Suruhanjaya Perkhidmatan Air Negara (SPAN), “C.5.2 Use of Non-Potable Water,” in Uniform Technical Guidelines Water Reticulation And Plumbing, Suruhanjaya Perkhidmatan Air Negara (SPAN).

[3] Taylor, J., McLoughlin, R., Sandford, J., Bevan, R. and Aldred, D., 2020. Legionella species: A potential problem associated with rain water harvesting systems?. Indoor and Built Environment, 30(6), pp.801-815.

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