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Selecting an appropriate size for domestic rainwater tanks in Colombo

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conference contribution
posted on 12.02.2018, 15:08 by Guna Hewa, David Pezzaniti, Simon Beecham, Kapil Gupta
Both India and Sri Lanka have experienced rapid population growth and migration to the major cities in the past decade. This rapid urbanisation has resulted in overstressing of existing water supply systems, with a loss of recharge areas and an increased depletion of groundwater. These effects have further aggravated the urban water crisis. During the monsoons, the existing drainage systems are overloaded and overflow thereby resulting in flooding causing severe damage to property. Sewage overflows often lead to the outbreak of epidemics and occasionally to the loss of life. Rainwater harvesting systems serve the dual purpose of water storage to reduce urban runoff peak flows as well as augmentation of the existing water supply systems. To achieve minimum costs while optimising the security of supply, rainwater tanks need to be sized taking the local rainfall conditions into consideration. This paper presents a methodology to determine the optimal size of rooftop storage based on historical rainfall data. Annual savings of in-house demand as well as the security of rainwater supply are discussed. The methodology is applied to Colombo in Sri Lanka. A case study is based on 150lpd household demand with 25m2 of roof area in Colombo. The appropriate rainwater tank is determined to be 2000 L in capacity. The resulting water saving is 54% of annual in-house demand and more importantly, zero supply from the tank happens during only one third of the year.



  • Architecture, Building and Civil Engineering

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  • Water, Engineering and Development Centre (WEDC)

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WEDC Conference


HEWA, G. ... et al, 2006. Selecting an appropriate size for domestic rainwater tanks in Colombo. IN: Fisher, J. (ed). Sustainable development of water resources, water supply and environmental sanitation: Proceedings of the 32nd WEDC International Conference, Colombo, Sri Lanka, 13-17 November 2006, pp. 445-450.


© WEDC, Loughborough University


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This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

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