During 1986–1991 a survey of 30 physicochemical parameters was
conducted in waterworks throughout Norway, selected to represent
the general population [27]. Personnel at the waterworks were asked
to collect samples of raw and treated water. All together 566 waterworks,
supplying 64% of the population, provided samples. Over time,
several smaller waterworks were incorporated into larger ones,
resulting in a total of 429 waterworks included in this study. The sampling
and analysis procedures are described elsewhere