Validation and verification

Validation and verification are important to establish that components within the
water safety plan are working as expected and that the water safety plan as a whole is
delivering the required results.
11.1 VALIDATION
Validation should be targeted at the assessment of the scientific and technical inputs
into the water safety plan. Validation should ensure that the information supporting
the plan is correct and that the elements
of the water safety plan will be
effective, thus enabling conformity with
health-based targets (see Chapter 12)
and public health policy.
Process validation is required to
show that treatment processes can operate as required. It can be undertaken during
pilot stage studies, during initial implementation of a new or alternative water
treatment system and is a useful tool in the optimisation of existing treatment
processes. Table 11.1 details the validation of the critical limits, relating to
coagulation and flocculation, for the Molendinar water purification plant, operated by
Gold Coast Water (Australia),Evidence for validation of the water safety plans can come from a variety of
sources, including the scientific literature, trade associations, regulation and
legislation departments, historical data, professional bodies or supplier knowledge.
This can inform subsequent testing requirements, including the use of specific
pathogens or indicator microorganisms. Microbial parameters, such as heterotrophic
plate counts and coliform enumeration, which may be inappropriate for operational
monitoring, can be used for validation purposes and the design of treatment systems
as this does not form part of the routine day-to-day monitoring and management and
thus the lag time in receiving the results is not a problem.
11.2 VERIFICATION
Verification may include review of monitoring control measures, microbiological and
chemical testing, or review of the water
safety plan overall to ensure that it is
still accurate. This may be necessary,
for instance, if there have been changes
to processes or equipment.
To verify system performance, periodic checks are necessary.
11.2.1 Microbial water quality
For microbial quality, verification is likely to include some microbiological testing. In
most cases it will involve the analysis of faecal indicator microorganisms (for further
details see Dufour et al. 2003), but in some countries it may also include assessment
of specific pathogen densities. Verification for microbial quality of drinking-water
may be undertaken by the supplier, surveillance agencies or a combination of the two.
Approaches to verification include testing of source water, treatment end-point
product and water in distribution systems or stored household water. Verification of
microbial quality of drinking-water includes testing for Escherichia coli as an
indicator of faecal pollution. E. coli provides conclusive evidence of recent faecal
pollution and should not be detected. In practice, the detection of thermotolerant
coliform bacteria can be an acceptable alternative in many circumstances. While E.
coli is a useful indicator it has limitations. Enteric viruses and protozoa are more
resistant to disinfection and consequently the absence of E. coli will not necessarily
indicate freedom from these organisms. Under certain circumstances it may be
desirable to include analysis for more resistant microorganisms such as
bacteriophages and/or bacterial spores. Such circumstances could include the use of
source water known to be contaminated with enteric viruses and parasites or high
levels of viral and parasitic diseases in the community.
Water quality can vary rapidly and all systems are subject to occasional failure. For
example, rainfall can greatly increase the levels of microbial contamination in source
waters and waterborne outbreaks often occur during and shortly after storms. Results
of analytical testing must be interpreted taking this into account.
11.2.2 Chemical water quality
Assessment of the adequacy of the chemical quality of drinking-water relies on
comparison of the results of water quality analysis with guideline values. For
additives, i.e., chemicals deriving primarily from materials and chemicals used in the
production and distribution of drinking-water, emphasis is placed on the direct control
of the quality of these products. In controlling drinking-water additives, testing
procedures typically assess the contribution of the additive to drinking-water and take
account of variations over time in deriving a value which can be compared with the
guideline values.
Some hazardous chemicals that occur in drinking-water are of concern because of
effects arising from single exposures or sequences of exposures over a short period.
Where the concentration of the chemical of interest varies widely, even a series of
analytical results may fail to fully identify and describe the public health risk. In
controlling such hazards, attention must be given to both knowledge of causal factors
and trends in detected concentrations, since these will indicate whether a significant
problem may arise in the future. Other hazards may arise intermittently, often
associated with seasonal activity or seasonal conditions. One example is the
occurrence of blooms of toxic cyanobacteria in surface water.
11.4 KAMPALA CASE STUDY – VALIDATION AND
VERIFICATION
In Kampala, a risk assessment was performed on the system to assess current
performance and as a means of validating whether the water safety plan would deliver
water considered safe (Howard and Pedley 2003). The assessment took the form of
assessment of removal of selected microbial indicators and index organisms through
the treatment works (E.coli, Clostridium perfringens and coliphage) and analysis of
indicator organisms (E.coli and faecal streptococci) in the distribution system. A
quantitative risk assessment was performed, using a well-defined set of assumptions
regarding the relationship between organisms analysed and pathogen groups. The
process utilised the simplified methodology outlined in the WHO Guidelines for
Drinking-Water Quality, 3rd edition (WHO 2004).
The assessment demonstrated that effective implementation of the water safety
framework ensured adequate bacterial quality from the treatment works, although as
the source water was of high quality this was expected. The assessment demonstrated
that risks were much greater in the distribution system and therefore emphasised the
need for improved safety management within the network following the water safety
plan.
The assessment did indicate that the treatment works provided far less security
regarding the risk from protozoan pathogens, a result again expected given that the
plants were not designed with protozoa removal in mind. It was concluded that
greater security could be obtained in one treatment works through better operation,
but in the second investment would be required to upgrade the system. However,
bearing in mind that overall rates of connection were low, alternative supplies were
grossly contaminated and that poor hygiene and inadequate sanitation were likely to
account for a greater proportion of pathogen transmission, it was recommended that
such investment was a relatively low priority.
Verification is achieved through a number of mechanisms. At the treatment works,
a regular programme of testing for E.coli was established (following previous
practice, but with reduced frequency) and the laboratory was equipped to perform
analysis of Clostridium perfringens as a means of testing treatment efficiency.
Treatment plant audits are also undertaken on a regular basis to review operational
records.
A rolling programme of testing for E.coli and sanitary inspection is also
implemented for the distribution system. Periodic testing of faecal streptococci is also
performed. These processes provide the water quality control department with data on
which to ensure that the water safety plan is delivering safe drinking-water and can be
incorporated into periodic risk assessments using available data.