57efficiency can translate 80–90 % of incident rainfall into runoff. Most of the rainwa-
ter is only available for a short period of time, either during the rainfall or immedi-
ately afterward. This method involves a catchment area from one or more roofs, a
storage tank, and gutters and pipes to guide the water from the roof into the storage
tank. A tap is often attached to the tank to access the stored water (Fig. 3 ). Rope and
pully arrangements or simple rope and bucket arrangements also work. This method
is suitable for humid, semiarid and arid regions. Rooftop WH is practiced in many
countries while in others it is not common; the main concerns are with traditional
roofing materials, water quality, and the cost of the storage tank. Social traditions
also discourage rooftop WH in some areas. There is concern over whether the water
is clean enough for drinking as pollutants in the atmosphere can be present in rain-
fall. Today, water harvesters must be wary of pesticide contamination, high mineral
levels, bacteria and other impurities in their runoff water (Palmback 2004 ).
Increasing pressures from water scarcity and rising awareness, development of
roofing materials, and innovative ideas for water storage have made roof water har-
vesting a serious, feasible and attractive option for water resource availability. An
increase in the adoption of rooftop WH requires low-tech and low-cost means of
Fig. 3 Rooftop water harvesting in Beypazari in Turkey (top left), Brazil (top right) and Ethiopia
(bottom) (Source: Akhtar Ali personal communication)
Water Harvesting in Dry Environments