Variability of mineral intakes from drinking water: a possible explanation for the controversy over the relationship of water quality to cardiovascular disease.

The assumption that people using the same water supply have similar intakes of minerals from drinking water is examined. Duplicate samples of all water drunk during a 24 hour period, including that boiled for beverage preparation, were collected by 109 adult subjects. The results showed that there may be more than a tenfold variation in the amount of water people drink daily. In addition it was found that the mineral concentrations in the 24 hour samples can vary markedly from those in water collected from the source or supply or from household taps which are the usual sampling points for epidemiological studies. The convention of using total hardness as an indicator of mineral intakes from hard and soft water is questioned.

Estimations of daily mineral intakes from drinking water.

Duplicate samples of all tap water drank over 24 h, including that used for beverage preparation, were collected from 109 adult subjects. There were more than ten-fold variations in daily water intakes. The mineral concentrations in the 24-h samples from households on the same public water supply showed considerable variation, the differences sometimes being greater than those found in water samples from different sources. These findings raise considerable doubt about the accuracy of accepted methods for the estimation of mineral intakes from drinking water. Although the mineral concentrations in water samples were generally very low some subjects received 10 per cent or more of their recommended dietary intake of Cu and Zn from this source. The implications of the findings are discussed.