rapid assessment of drinking-water quality in the republic of tajikistan

2 Methods
2.1 Survey design
The methodology for the RADWQ pilot project is detailed in the handbook, Rapid assessment of
drinking-water quality: a handbook for implementation (Howard et al., 2003). In essence, the method
involves selecting representative sampling points using a statistically-based survey; analysing the
water quality for a suite of parameters; carrying out sanitary inspections at the selected sampling
points; analysing the data and its relation to historical data; and making conclusions and
recommendations. There are six countries in the pilot study and data from each will be presented in
individual country reports (of which this is one) and in an overall summary report.
The survey design selected for the RADWQ project uses a cluster sampling approach to identify the
number, type and location of water supplies to be included in the assessment. Cluster sampling means
that the water supplies selected for inclusion in the assessment are geographically close to one another
(in “clusters”), but are representative of all water-supply technologies. This approach was selected for
RADWQ as it is used in other international surveys addressing water, sanitation and health (such as
the Multiple Indicator Cluster Survey) that contribute to the WHO/UNICEF JMP. In addition, cluster
sampling improves the efficiency of the assessment by making access to the water supplies easier and
by reducing costs.
The key element of the survey design is to ensure that the selection of the water supplies to be
included reflects their importance; therefore only improved technologies supplying more than 5% of
the population are included. The basic sampling unit is the water supply, rather than the households
that use them. The rapid assessments are primarily designed to assess the quality and sanitary
condition of the water supplies and hence the risk to water safety. A limited analysis of water stored
in households, matched to water sources, is included in the assessment.
The number of water samples to be taken was calculated using Equation 2.1:
4P(1
P)
D 4*0.5(1 0.5) * 4
n 1600
(Equation 2.1)
2
2
e
0.05
n =
P =
D =
e =
required number of samples;
assumed proportion of water supplies with a water quality exceeding the water-quality
target(s) established;
design effect;
acceptable precision expressed as a proportion.
For the RADWQ pilot project, the proportion was assumed to be 0.5, with a precision of ±0.05 and a
design effect of 4. This gave the number of water supplies to be included within each country
assessment as 1600 (Equation 2.1). The steps of the rapid assessment are summarized in Figure 2.1
and the steps in survey design are summarized in Figure 2.2. The range of parameters tested and the
inspections undertaken are shown in Table 2.1.
2.2 Country-specific survey design
A training workshop on the survey methodology was conducted on the 1516 September 2004,
followed by several meetings of a core technical working group for in-depth discussions about the
data and the design of the survey for specific countries. A Russian translation of all training materials
and the RADWQ methodology was available at the time of training.
A summary of the country-specific survey design is shown in Table 2.2 and Figure 2.3, and the
frequency of testing for individual parameters is shown in Table 2.3. The individual steps used to
design the survey are documented in Annex 4. A more detailed explanation of the survey design in
Tajikistan follows.
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