Newsletter and Technical Publications
of Alternative Technologies for Freshwater Augumentation
Countries in Asia>
1.1 Dual Water Distribution System
Water reuse, and the reuse of wastewater in particular, is receiving
increasingly wide attention, even though it is often considered to be of
marginal quality. Use of treated wastewater through dual water
distribution and plumbing systems can provide a secondary source of water
for purposes such as irrigating private gardens and toilet flushing. The
provision of waters of lesser quality through a separate distribution
system for non-potable purposes from alternative sources of supply can
help lower the demand for potable freshwater. Application of this
technology is largely a matter of cost, acceptance and practice, as the
distribution technology involved is not significantly different in dual
distribution systems compared to conventional single distribution systems.
In the Kathmandu Valley, where water scarcity is increasing, conjunctive
use of shallow groundwater sources for toilet flushing and washing of
clothes, together with potable water supplied through the municipal water
supply system for other purposes, is being practised in residential areas.
A rower pump (hand pump) is fitted to a 3.8 cm diameter polyvinylchloride
pipe ranging from 6 m to 15 m in length which is driven to the ground.
Water from the groundwater source thus tapped is pumped manually whenever
Extent of Use
This technology is widely used in the Kathmandu Valley in locations
where the groundwater table is within 15 m of the ground surface. It is
also popular in locations where the municipal water supply is
intermittent. People of low income are increasingly using this technology
in preference to the higher cost municipal supply.
Operation and Maintenance
The operation and maintenance of dual distribution systems is simple,
and involves keeping the pipe and the pump clean. Maintenance consists of
changing the pump washer once a year or whenever it starts leaking. No
additional maintenance of the municipal supply system is required, and no
changes in municipal distribution system operation are necessary.
Level of Involvement
Providing dual distribution systems at the household level requires no
external involvement relative to the groundwater sourced portion of the
system. The municipal sourced portion of the system is generally
constructed and operated by the local governmental unit.
The total cost of the groundwater sourced portion of the system is about
$55 for a 10 m deep well.
Effectiveness of the Technology
This technology has helped alleviate the problem of water scarcity in
Kathmandu. For an average household, more than 60 % of the annual
household water requirements is met by using shallow groundwater, which is
of lower quality than the municipal water, for non potable purposes.
Water supplied from the rower pump can be used for toilets, bathing,
gardening, car washing, and similar purposes. The dual distribution system
is most suitable for use in areas where the groundwater is within 15 m of
the ground surface; otherwise, a mechanical pump will be necessary, adding
to the cost of the groundwater sourced portion of the system.
This technology is inexpensive and can be constructed using
locally-available technology. Water is made available whenever needed, and
use of the dual sourced system eases the water scarcity problem not only
at the household level but also throughout the entire city.
Conjunctive use of dual sourced water may be limited as a result of poor
water quality. Water drawn from alternative sources may not be used for
drinking even after boiling because of odours and tastes associated with
groundwater. Further, such water may pose severe health hazards if the
abstraction point is located too close to septic tank outflows. The
possible high nitrate concentrations and bacterial levels that may be
present in surfacial groundwaters may also lead to health hazards when
used by poor people and children for drinking purposes. Widespread use may
contribute to a decline in the groundwater table (due to over
exploitation). Also, water logging and mosquito breeding in the pump area
may occur if proper drainage is not provided.
No cultural problems have been noted, although use may be limited due to
odours associated with the groundwater.
Further Development of the Technology
This technology will be more attractive and useful if simple and
inexpensive electric motors are attached to the tubewell and the
groundwater sourced portion of the system is fully incorporated into the
household water supply system.
Dirgha Nidhi Tiwari, Koteswar, c/o Post Office Box EPC
4000, Kathmandu, Nepal. Tel. 977 1 410249, E-mail: email@example.com.