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In designing a rainwater harvesting system if we provide tanks on the ground level, we would have to provide a proper pumping system to use the water  harvested - here there is additional cost  involved in providing the pumping system and also the electricity cost. There is also a maintenance cost involved. But the water tank can be provided in an open space available.

If we provide an elevated water tank- either by providing a space in the building at a higher floor or providing a separate structure for supporting the water tank - there is no pumping & electricity cost  because water can gravitate to needed areas - but there is a cost of providing a room or a separate structure (surely more expensive).

Has any study been made to find out which of the system is more cost effective?
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3 Answers

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Best answer
Mr.Harjit Singh,

The first question that we should  ask is what are we going to do with the harvested rainwater? if you are using it for watering plants in garden or washing of drains, etc then the best option will be the gravitated system where the filtered water is piped to various taps for use. But if the treated rain water is recircle for internal building usage such urinal & flushing system then a pumping system will be the only option you have to ensure sufficient flow & pressure to the various fittings and outlets.

The decision on  the type of usage and design capacity of rainwater tank must be made at an early stage of  design development to ensure all HODTs are aware of the requirements and be able to provide appropriate provision for this system. Generally sustainable design means use less water and less electricity in this context therefore the use of pumps to pressurize rainwater for usage must be avoided unless you are using for internal building system.

Design the building with gravitated rainwater system and with proper arrangement and location of rain water tank the initial installation cost can be minimal and maintenance free ( just require regular routine cleaning of debris & tank)  whereas in the pumping system it will be a liability to building owner to maintenance  and take note the  cost of electricity is spiralling upwards and the efficiency of pump & motor will reduce over time and obviously longer "break even" duration.

In designing rainwater harvesting system , please follow the simple principle that is to " Keep it Stupity Simple"
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3 votes
i think client most prefer gravity method because Return of Investment can be shorten. Monitoring using flow meter (RWH) and then convert to RM equal to savings n then minus with electricity usage to operate pump. If there is no saving at all or return period too long after considering maintenance cost etc better consider gravity method only.

i'm not an expert but just from my opinion thru reading.
9,530 points 25 58 109
4 votes

Mr Harjit Singh Sir,

Its quite difficult to giv one absolute correct answer coz everyone of them has their own advantageous and disadvantageous.

Nevertheless i would like to share some notes here with u that might shed some light,


Rainwater Harvesting - Pumps or Pressure Tanks
by Doug Pushard

If you are building or planning to install a rainwater collection system, water pressure (i.e. water line pressure) is one of the main issues you need to think about. There one several ways to achieve water pressure when you turn on the faucet. One is gravity. Another is installing a pump to ensure water pressure in your water lines. If gravity does not work for you, you will need to install a pump and there are several options to consider, some new and some old.

System components change over time, but system designers or installers might not change at the same pace. Sometimes it is the old adage “if it ain’t broke don’t fix it”, but it also could be just resistance to new ways or lack of information on why and when to change. Is this the case with new pressure sensitive pumps versus pressure tanks

In designing a system, sometimes it is one aspect of the overall rainwater system that makes one option better than another. Is this the case with the brand new inline pump controllers versus pressure sensitive pumps?

Pressure tanks have been around for a long, long time and have typically been installed on wells and whole-house rainwater catchments systems (i.e. households with no other water system). The tanks hold water for immediate use; consequently, there is no lag in turning on the tap and water coming out the spout as there would be with a standard pump.

Pressure-sensitive pumps are newer and sense the pressure in the water line and turn on when there is a pressure drop in the line (i.e. when the faucet is turned on). Both pressure sensitive pumps and pressure tanks work to accomplish the same end - water at the tap when required.

Newest of all, are inline pump controllers. These are a separate device (i.e. not integrated into the pump) that sense line pressure and turn on the pump. Inline controllers can be easily added to existing installations.

So with three different options, which is best? The short answer is - it depends.




Back to your question, which is most cost effective between gravity and the pumps that is mentioned above,  i dun hav any straight answers.


Anybody can enligthen us on this?. Perhaps our Pengarah Kanan  Senggara & Fasiliti jalan boleh membantu, coz he's an expert in water and he once headed the Water Department. Hope he can share with us the pros and cons on this gravity and pump.


اللهمّ يسر و لا تعسر








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