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 drinkingwater
and take account of variations over time in deriving a value that can be
compared with the guideline value (see section 8.5.4).
As indicated in chapter 1, most chemicals are of concern only with long-term exposure;
however, some hazardous chemicals that occur in drinking-water are of concern
because of effects arising from 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 (e.g., nitrate, which
is associated with methaemoglobinaemia in bottle-fed infants). In controlling such
hazards, attention must be given to both knowledge of causal factors such as fertilizer
use in agriculture 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.
A
,
