d>
7. Water supply
92
7.
Water supply
7.1
Water-supply preparedness and protection
Water-supply problems arise in all phases of the disaster-management cycle. As with all
other elements of emergency management, water supplies can be designed and main-
tained in ways that help to reduce the health impacts of disasters.
It is useful to distinguish between large-scale, formal water-supply systems (e.g. urban
water-supply systems) and small-scale, scattered supplies. The distinction is not so much
between urban and rural areas, as one based on the level of technology and the insti-
tutional arrangements for management, maintenance, and protection. Whether the
affected systems are rural or urban, sanitation surveys may be necessary to identify the
main health hazards (World Health Organization, 1997a).
Water sources are exposed to a variety of hazards that may damage or contaminate
them, but they can be protected against disasters to some extent. This section is con-
cerned mainly with ways in which improvements to existing water supplies can make
them more resistant to damage.
7.1.1
Establishing and protecting small-scale decentralized supplies
Kinds of damage to small-scale water supplies
Roof catchment systems are often damaged by wind in tropical storms. People who
depend on canals are vulnerable to chronic and acute pesticide poisoning or, where the
canal drains an industrial zone, poisoning from the release of toxic chemicals. Unlined
canals may also be easily washed away or broken during oods, so cutting water supplies.
Shallow wells in areas with a high water-table are more prone to contamination from
ooding than are deep boreholes. They may also dry up sooner in a drought. Hillside
springs may be destroyed in a landslide. Wells near rivers can be contaminated and lled
with sand during unusual ash ooding. All piped systems are subject to breaks and dis-
ruption during earthquakes, landslides or civil strife. Dug wells and boreholes are par-
ticularly vulnerable during wars, since bodies or toxic materials can be dumped in wells,
and borehole pumps sabotaged.
Routine forms of protection
In all activities to provide or improve water supplies during normal times, it is impor-
tant that those responsible are aware of the specic hazards to which water sources might
be subject. This hazard mapping should be as much a part of the planning of water-
supply systems as other factors, such as water quality and taste, distance to users, and
capital and recurrent costs.
Simple modications in design can sometimes help to protect the water source from
an extreme natural event or industrial accident. For instance, exible plastic pipe is more
resistant than rigid pipe to earth tremors.
Some basic improvements, such as raising the head wall of a dug well, and providing
a cover and outward-sloping concrete apron around it, simultaneously provide additional protection from contamination due to oods and run-off into the open hole, and short-
circuit seepage from nearby puddles; they also prevent contamination by debris and
animals falling into the well.
If the surface or groundwater could be affected by toxic hazards, it is probably better
to avoid the water source. Providing an alternative water source should then be a high
priority.
Need for consultation with water users
Many people use multiple sources of water. Some will prefer certain sources for drinking-
water and others for laundry, bathing, watering animals and irrigation.
Wherever a hazard, or the potential for disruption of the water supply, exists, the
primary health-care workers or other development personnel should discuss alternative
drinking-water sources with the people concerned. These discussions should take place
before an emergency arises. A delegation from the local health committee or safety com-
mittee should visit the alternative sources regularly to check on their status. Where recent
improvements in water supply have resulted in former sources being abandoned, the
committee may want to discuss the desirability of providing some minimal maintenance
at the old site to preserve it for use in an emergency.
There should also be local contingency plans for rapidly ensuring the safety of such
reserve sources of drinking-water. These will usually involve stockpiling a limited amount
of chemicals to disinfect the source (taking into consideration the shelf-life of these
chemicals), plus fencing to exclude animals. Depending on the economic base of the
community or neighbourhood concerned, the discussion may go on to consider the pro-
vision of alternative or reserve water for livestock, small-scale industry, or irrigation;
however, the rst priority should always be water for drinking, cooking and personal
hygiene.
7.1.2
Establishing and protecting large-scale, centralized supplies
Types of hazard
The location of sources and the design of water-supply systems are critical in emergency
and disaster preparedness. Hazards to catchments (e.g. forest res or chemical conta-
mination), reservoirs (drought, earthquake, contamination, landslides), pumping and
treatment plants (ood, earthquake, re, explosion, chlorine gas leaks), as well as to the
distribution system (earthquake, ooding), need to be taken into account in siting,
design and contingency planning. Sabotage may pose a hazard to all stages of a water-
supply system.
Strengthening existing systems
Weak points in distribution systems, such as river crossings, open canals, landslide scars,
etc., or places where pipes cross earthquake faults, should be strengthened (see Figure
7.1). Low-lying, ood-prone facilities can be raised or protected with levees or bunds.
Reserve electrical generators can be provided if necessary, as well as a stock of pre-
positioned replacement pumps and pipes for emergency repairs. Standardization of
pumps, pipes and ttings, etc. is important, so that spares and equipment can be sent
as temporary replacements from an unaffected town.
Systems based on rapid sand ltration can be made less vulnerable to disasters by
appropriate staff training and by including emergency provisions at the planning stage
that will help cope with prolonged high turbidity, power failures and shortages of chem-
icals. Emergency provisions include extra stocks of chemicals, stand-by power generators
and emergency preltration storage/sedimentation capacity.
7
: WATER SUPPLY
93 Staff should be rigorously trained in the action to be taken in an emergency to assess
the state of the water-supply system and to restore and ensure its integrity from the stand-
point of health and the environment.
Long-term investment decisions
Long-term design and investment decisions should also take into account the possibil-
ity of disaster. For instance, slow sand lters, which can be adequate even for large cities
(e.g. London and Amsterdam), are less vulnerable than other treatment systems to
hazards, such as interruption of chemical supplies and power supplies (Pickford, 1977).
Decisions on routing water-transmission mains and distribution networks should also
take into account the possibility of damage due to natural causes, such as earthquakes
and landslides, and to sabotage.
7.1.3
Preparation for displacement emergencies
When a risk of population displacement is identied in the vulnerability assessment (see
Section 3.3), steps should be taken to prepare for such an event, taking into account the
likelihood of displacement, the likely numbers of displaced people, displacement routes,
and likely destinations. Preparedness measures may include: identifying water sources
along displacement routes and at potential temporary settlements; pre-positioning stocks
of lightweight water equipment (pumps, exible reservoirs, pipes and taps) and supplies
(fuel and water treatment chemicals); identifying and training staff; and holding dis-
cussions with local communities along displacement routes about access to water sources.
During a large population movement, it may be very difcult to move staff and equip-
ment along the congested roads, so it is important to establish a local response
capacity.
7.2
Emergency water-supply strategy
7.2.1
Situations demanding an emergency water-supply response
Short-term water-supply needs and emergency measures may differ in the following types
of situations:
short-term emergencies affecting rural or unserved periurban communities;
short-term emergencies in urban situations where a central water service is
available;
short-term emergencies involving population displacement and temporary
shelters;
ENVIRONMENTAL HEALTH IN EMERGENCIES
94
Figure 7.1 Reinforcement of water pipes crossing streams or gullies
1
1
Sources: American Water Works Association (1984), Jordan (1984). long-term displacement emergencies that result in semipermanent emergency
settlements.
These situations are considered in turn in sections 7.2.37.2.7.
7.2.2
Emergency response strategy
Priorities
The rst priority is to provide an adequate quantity of water, even if its quality is poor,
and to protect water sources from contamination. A minimum of 15 litres per person
per day should be provided as soon as possible (Sphere Project, 2000), though in the
immediate post-impact period, it may be necessary to limit treated water to a minimum
of 7 litres per day per person (United Nations High Commissioner for Refugees, 1992a).
If this is the case, then people may use an untreated water source for laundry, bathing,
etc. Water-quality improvements can be made over succeeding