multiplying the number of units in each category
by the average roof area of that category, while
for apartments in multi-storey residential buildings,
the total area is divided by 6, assuming that
the typical multi-storey building has six floors.
Tables 4a and 4b present the total roof area for
both Amman (14.43×106 m2) and Irbid (10.04×
106 m2) governorates. The same procedure is
followed for the other governorates. Total roof
area for each governorate is shown in the second
column of Table 5. The calculated total roof area
is required to estimate the volume of rainwater
that could be harvested in each governorate.
In this paper, water harvesting yields are
calculated for residential roofs including single
houses, villas, and apartments for the twelve governorates
in the kingdom. Monthly rainfall data
were obtained from the Ministry of Water and
Irrigation [12]. The average monthly rainfall data
for each governorate are shown in Table 3. The
volume of rainwater that could be harvested in
each of the 12 governorates was calculated
considering the annual rainfall data, the total roof
area, and a run-off coefficient of 0.8. Such a runoff
coefficient indicates a loss of 20% of the
rainwater that is discarded for roof cleaning and
evaporation. Thus, the volume of rainwater that
could be harvested in each governorate was
determined by using Eq. (1).
VR = (R × A× C/1000) (1)
where VR is the annual volume of rainwater that
could be harvested in each governorate, R is the
average annual rainfall in each governorate
(mm/y), A is the total roof area in each governorate
(m2), C is the run-off coefficient (nondimensional),
and 1000 is the conversion factor
from mm to m [13].
Then, to obtain potential annual water savings,
water demand was compared to the volume of
rainwater that could be harvested in each
governorate. The annual potential for potable
water savings was determined for each of the 12