Affordable Roofwater Harvesting Thomas & Rees 1 Affordable Roofwater Harvesting in the Humid Tropics

The relatively high cost per household of installing full domestic roofwater harvesting (DRWH) has resulted in its take-up being largely limited to areas of especially high water stress or where DRWH is subsidised. The paper discusses various ways of attaining satisfactory benefit:cost ratios in areas where DRWH is not the only water supply option, for example by adopting partial or seasonal supply and by minimising ‘first cost ’ (generally construction cost) at the expense of raising subsequent costs. As water storage accounts for the bulk of expenditure on most systems, the paper then focuses on means of minimising the construction cost of storage tanks in the size range 1000 to 10000 litres. Best cost-cutting practices with respect to both surface and underground tanks are reviewed. An approach of separating the ‘structural ’ and the ‘water-proofing ’ roles of construction materials is proposed and applications of this approach to both sorts of tank are examined. The paper will particularly reflect experiences in South Asia and East Africa which are the geographical focus of an ongoing 4-country DRWH research programme funded by the European Union.