Answer & Explanation:
Ideally, a laboratory infrastructure should be established which will enable all
samples to be returned to a central or regional laboratory within a few hours of
being taken. However, this depends on the availability of a good road system and
of reliable motorized transport for all sampling officers, and these are not available
in many countries. Thus, although it may be possible to establish well-equipped
central and even regional laboratories for water analysis, at the provincial and
district levels it may be necessary to rely on a relatively small number of simple
tests. As noted in Chapter 1, this approach is sometimes called critical-parameter
water testing.
The most important factor to take into account is that, in most communities,
the principal risk to human health derives from faecal contamination. In some
countries there may also be hazards associated with specific chemical contami-
nants such as fluoride or arsenic, but the levels of these substances are unlikely to
change significantly with time. Thus, if a full range of chemical analyses is
undertaken on new water sources and repeated thereafter at fairly long intervals,
chemical contaminants are unlikely to present an unrecognized hazard. In con-
trast, the potential for faecal contamination in untreated or inadequately treated
community supplies is always present. The minimum level of analysis should
therefore include testing for indicators of faecal pollution (thermotolerant (faecal)
coliforms), turbidity, and chlorine residual and pH (if the water is disinfected
with chlorine).
Even in developing countries poorly served by roads and transportation, it is
usually possible to devise a rational sampling and analytical strategy. This should
incorporate carefully selected critical-parameter tests in remote (usually rural)
locations using simple methods and portable water-testing equipment (see pp.
65–66) where appropriate. Wherever possible the community should be involved
in the sampling process. Where water is disinfected, primary health workers,
schoolteachers, and sometimes community members can be trained to carry out
simple chlorine residual testing. The same people could also collect samples for
physicochemical analysis and arrange for their delivery to the regional laboratory.
The use of community members in this way has significant implications for
training and supervision but would be one way of ensuring more complete
surveillance coverage.
