373.1 Role and purpose of health-based targetsHealth-based targets should be part of overall public health policy, taking intoaccount status and trends and the contribution of drinking-water to the trans-mission of infectious disease and to overall exposure to hazardous chemicals both inindividual settings and within overall health management. The purpose of settingtargets is to mark out milestones to guide and chart progress towards a predeterminedhealth and/or water safety goal. To ensure effective health protection and improve-ment, targets need to be realistic and relevant to local conditions (including economic,environmental, social and cultural conditions) and financial, technical and institu-tional resources. This normally implies periodic review and updating of priorities andtargets and, in turn, that norms and standards should be periodically updated to takeaccount of these factors and the changes in available information (see section 2.3).Health-based targets provide a “benchmark” for water suppliers. They provideinformation with which to evaluate the adequacy of existing installations and policiesand assist in identifying the level and type of inspection and analytical verificationthat are appropriate and in developing auditing schemes. Health-based targets under-pin the development of WSPs and verification of their successful implementation.They should lead to improvements inpublic health outcomes.Health-based targets should assist in determining specific interventionsappropriate to delivering safe drinking-water, including control measures suchas source protection and treatmentprocesses.The use of health-based targets isapplicable in countries at all levels ofdevelopment. Different types of target will be applicable for different purposes, so thatin most countries several types of target may be used for various purposes. Care mustbe taken to develop targets that account for the exposures that contribute most to3Health-based targetsThe judgement of safety – or what is a tolerable risk in particular circumstances –is a matter in which society as a whole has a role to play. The final judgement as to whether the benefit resulting fromthe adoption of any of the health-basedtargets justifies the cost is for eachcountry to decide.GUIDELINES FOR DRINKING-WATER QUALITY38disease. Care must also be taken to reflect the advantages of progressive, incrementalimprovement, which will often be based on categorization of public health risk (seesection 4.1.2).Health-based targets are typically national in character. Using information andapproaches in these Guidelines, national authorities should be able to establish health-based targets that will protect and improve drinking-water quality and, consequently,human health and also support the best use of available resources in specific nationaland local circumstances.In order to minimize the likelihood of outbreaks of disease, care is required toaccount properly for drinking-water supply performance both in steady state andduring maintenance and periods of short-term water quality deterioration. Perfor-mance of the drinking-water system during short-term events (such as variation insource water quality, system challenges and process problems) must therefore be con-sidered in the development of health-based targets. Both short-term and catastrophicevents can result in periods of very degraded source water quality and greatlydecreased efficiency in many processes, both of which provide a logical and soundjustification for the long-established “multiple-barrier principle” in water safety.The processes of formulating, implementing and evaluating health-based targetsprovide benefits to the overall preventive management of drinking-water quality.These benefits are outlined in Table 3.1.Targets can be a helpful tool both for encouraging and for measuring incrementalprogress in improving drinking-water quality management. Improvements can relateto the scientific basis for target setting, progressive evolution to target types that moreprecisely reflect the health protection goals and the use of targets in defining and promoting categorization for progressive improvement, especially of existing watersupplies. Water quality managers, be they suppliers or legislators, should aim at con-tinuously improving water quality management. An example of phased improvementTable 3.1 Benefits of health-based targetsTarget development stage BenefitFormulation Provides insight into the health of the populationReveals gaps in knowledgeSupports priority settingIncreases the transparency of health policyPromotes consistency among national health programmesStimulates debateImplementation Inspires and motivates collaborating authorities to take actionImproves commitmentFosters accountabilityGuides the rational allocation of resourcesEvaluation Supplies established milestones for incremental improvementsProvides opportunity to take action to correct deficiencies and/ordeviationsIdentifies data needs and discrepancies3. HEALTH-BASED TARGETS39is given in section 5.4. The degree of improvement may be large, as in moving fromthe initial phase to the intermediate phase, or relatively small.Ideally, health-based targets should be set using quantitative risk assessment andshould take into account local conditions and hazards. In practice, however, they mayevolve from epidemiological evidence of waterborne disease based on surveillance,intervention studies or historical precedent or be adapted from international practiceand guidance.3.2 Types of health-based targetsThe approaches presented here for developing health-based targets are based on a con-sistent framework applicable to all types of hazards and for all types of water supplies(see Table 3.2 and below). This offers flexibility to account for national priorities andto support a risk–benefit approach. The framework includes different types of health-based targets. They differ considerably with respect to the amount of resources neededto develop and implement the targets and in relation to the precision with which thepublic health benefits of risk management actions can be defined. Target types at thebottom of Table 3.2 require least interpretation by practitioners in implementationbut depend on a number of assumptions. The targets towards the top of the tablerequire considerably greater scientific and technical underpinning in order to over-come the need to make assumptions and are therefore more
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