1.3.2 Health-based targets

Health-based targets provide quantifiable metrics for defining the safety of drinking water. In these Guidelines, health-based targets are based on health outcomes translated into performance targets for microbiological parameters, guideline values for chemical parameters and a reference value for radiological activity (Figure 1.3).

The health outcome for microbiological safety is an upper limit of 1 x $10^{-6}$ Disability Adjusted Life Years (1 µDALY) per person per year. The target is used as the basis for defining treatment performance targets based on source water quality as discussed in Chapter 5 and Appendix 3.

Health outcomes for chemical parameters (see Chapter 6) are based on:

• a NOEL (no observed effect level), LOAEL (lowest observed adverse effect level) or BMD (benchmark dose) for substances with a toxicity threshold

• cancer risk for genotoxic and carcinogenic substances that do not have a toxicity threshold (1 additional cancer per 1,000,000 people from a lifetime of exposure at concentrations above guideline value unless otherwise stipulated in these Guidelines) or

• a benchmark dose corresponding to a defined increase in an effect (between 1% and 10% but commonly 5%) from exposure of a population to a chemical.

These health outcomes are used to calculate health-based guideline values for individual chemicals.

The health outcome for radiological quality is based on minimising the risk of cancer from exposure to radiological elements in drinking water (see Chapter 9). This has been translated into a reference value of 1 mSv/year (ARPANSA 2017).

Figure 1.3 Health-based targets for microbial, chemical and radiological parameters

LRV – log₁₀ reduction value; DALYs - Disability Adjusted Life Years; pppy – per person per year; QMRA – quantitative microbial risk assessment; NOAEL – no observed adverse effect level; LOAEL – lowest observed adverse effect level; BMD – benchmark dose; μg/L – microgram per litre; Bq/L – becquerel per litre; mSv/year – millisievert per year.