Stochastic modelling of the hydraulic performance of an
onsite rainwater harvesting system in Mediterranean
climate
H. Muklada, Y. Gilboa and E. Friedler
ABSTRACT
The performance of onsite rainwater harvesting (RWH) system in Mediterranean climate was
assessed. A stochastic model quantifying the necessary storage, as a function of rainfall (frequency,
depth), roof area, residents’ number, specific water use (toilet flushing, laundry) and the required
efficiency was developed. Two performance indicators were calculated: water saving efficiency
(RSE) – proportion of water used supplied by the RWH system; and rainwater use efficiency (RUE) –
proportion of rainwater actually used. The maximum storage capacity and WSE decreased with
increasing number of residents for a given roof area, and with an increasing roof area for constant
number of residents. For variable storage volume, RUE increased with increasing storage capacity
and reached a maximum with an increase in residents’ number and a decrease in the roof area. The
model enables to determine WSE and RUE for specific storage volumes or to determine the desired
WSE and calculate the necessary storage.
H. Muklada
Y. Gilboa
E. Friedler (corresponding author)
Faculty of Civil & Environmental Engineering,
Technion – Israel Institute of Technology,
Haifa 32000,
Israel
E-mail: eranf@technion.ac.il
Key words | alternative water source, Mediterranean climate, rainwater harvesting, stochastic
modelling, water saving
INTRODUCTION
Onsite rainwater harvesting (RWH) is an ancient method
which served as an alternative source of water in many
places in the Middle East and all around the world. How-
ever, with the establishment of central water supply
systems, the use of onsite RWH systems has generally
stopped. Today due to increased water shortage on one
hand, and urban flooding on the other, there is a renewed
interest in onsite RWH. Interest in onsite RWH extends
from water-scarce regions where the motivation is increas-
ing the amount of available water, to water-ample ones
where the motivation is primarily prevention and reduction
of urban runoff as well as environmental awareness.
RWH has been acknowledged as a potential source to
supply water and to promote significant potable water savings
(Ghisi et al. ; Gires & de Gouvello ). Rainwater,
which is a renewable freshwater source, may be used in var-
ious non-potable applications at the household level in
urban areas. Rainwater, being the main source of freshwater
in both natural and human-managed ecosystems, has signifi-
cant untapped potential for being harvested (Umapathi
et al. ). Numerous studies investigating the harvested rain-
water quality were conducted in Australia, Canada, Denmark,
Germany, India, Japan, Spain, New Zealand, Thailand, and
the United States (Uba & Aghogho ; Evans et al. ;
Despins et al. ; Jones & Hunt ; Farreny et al. ).
However, less information and clear definition on rainwater
tank sizing are available (Ghisi ; Ward et al. , ;
Campisano & Modica ). The correct tank sizing is impor-
tant in order to avoid extra costs when the tank is oversized
and low efficiency when it is undersized. Several tools were
developed for estimating the required tank size and to predict
the system performance. For instance, Jenkins et al. ()
developed two behavioral algorithms to describe the oper-
ation of a RWH system during a given time interval. The
1614 © IWA Publishing 2016 Water Science & Technology: Water Supply | 16.6 | 2016
doi: 10.2166/ws.2016.082
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