Environmental Engineering Reference
In-Depth Information
Table 1 Bene
ts of rainwater harvesting
Short-term bene
ts
Long-term bene
ts
Meet water demand when no other
water sources are available
Reduced storm water run-off leading to lower energy
consumption for storm water treatment
Reduction of water demand
Use of harvested rainwater for aquifer recharge and
increase of depleted groundwater table
High
collection
and
distribution
Reduction of diffuse pollution resulting in improvement
of aquatic ecosystems
efficiency
Self-suf
ciency (less dependency on
distant watercourses)
Potential for lower consumer water bills
Reduction of
flood risk (reduction of
economic losses)
Greater
flexibility of a decentralised system consisting
of numerous water resource points in case of a natural
disaster rather than a centralised water supply system
that may collapse or go out of order
Enhance rational utilisation of water
through decentralised systems
found to be the most expensive practice, with related costs to be around
25
-
40 % of the total annual cost, followed by administration and inspection
costs (8
-
35 % of total annual costs), while tree planting cost was estimated to
be 2
-
15 % of total annual urban forestry expenditures.
4 Rainwater Harvesting
Rainwater harvesting (RWH) is a decentralised technique of collecting and storing
rainwater for later use at or near the point where water is needed or used providing
multiple bene
ts (Table
1
). Depending on scale, requirements and purpose, RWH
systems can range from low storage capacity (50
-
100 gallon) systems (e.g. rain
barrels) to larger systems (1,000
100,000 gallons) (US EPA
2013
). Rain barrels
can be easily placed outside buildings, with no connections to internal or external
plumbing, where rooftop run-off from downspouts is captured for later use mainly
for outdoor purposes, such as car washing and irrigation. Higher volume systems (e.
g. cisterns) collect storm water from roofs and other surfaces (e.g. parking lots,
terraces), and after quality treatment provide water to a distribution system. Har-
vested water can be used outdoors (e.g. landscape irrigation, fountains) or indoors
(e.g. toilet
-
flushing, clothes washing).
A typical RWH system is mainly comprised of the catchment area upon which
the rain falls; storage tanks and cisterns; gutters and downspouts to transfer rain-
water from the catchment area to the storage system; a
filtering system to remove
debris, solids and other materials; a monitoring system (e.g. for monitoring the
water level inside the tank) and a system to convey water for further use (e.g.
gravity system or pumps). The main issues emerging when constructing an RWH
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