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The Rainwater Harvesting Ladder

D. Brett Martinson and Terry Thomas

12th International Rainwater Catchment Systems Conference, New Delhi, India, 2005

The two most important barriers to further roofwater harvesting at the household level are high cost and inadequate service. Systems are too expensive for householders to afford them or, if the capacity is reduced to an affordable level, it is seen as too small to provide adequate service. As the cost of a rainwater harvesting system is a function of its capacity, these two problems are heavily interrelated.

For some years there has been in existence a “sanitation ladder”, a catalogue of designs of varying quality from which a project manager, a community or individual can select an appropriate well designed sanitation system to suit local conditions and the available funds. Such “ranges” are the norm in consumer products and usually form the basis for consumer choice.

Rainwater harvesting systems are very amenable to this product-range approach, as no account of local geology and topography need be taken: the water simply falls from the sky. They are however, slightly more complex than sanitation systems as there are, in effect two ladders, one for service provision – mainly a function of system size and one for quality of construction. It is in fact this quality aspect that is predominant in the sanitation ladder whereas roofwater harvesting systems are dominated by the question of size with a certain quality taken as read. Systems of different sizes and qualities can be clearly presented alongside forecasts of the service they will provide and a community can decide on the solution that is best for them. This paper describes the making of such a ladder for presentation to a community.

 

Full paper available from the conference site

Full paper as a final draft submitted for publication (18pp, 720kb) (PDF Document)