The mineral content of tap water in United States households

The composition of tap water contributes to dietary intake of minerals. The Nutrient Data Laboratory (NDL) of the United States Department of Agriculture (USDA) conducted a study of the mineral content of residential tap water, to generate current data for the USDA National Nutrient Database. Sodium, potassium, calcium, magnesium, iron, copper, manganese, phosphorus, and zinc content of drinking water were determined in a nationally representative sampling. The statistically designed sampling method identified 144 locations for water collection in winter and spring from home taps. Assuming a daily consumption of 1 L of tap water, only four minerals (Cu, Ca, Mg, and Na), on average, provided more than 1% of the US dietary reference intake. Significant decreases in calcium were observed with chemical water softeners, and between seasonal pickups for Mg and Ca. The variance of sodium was significantly different among regions (p < 0.05) but no differences were observed as a result of collection time, water source or treatment. Based on the weighted mixed model results, there were no significant differences in overall mineral content between municipal and well water. These results, which are a nationally representative dataset of mineral values for drinking water available from home taps, provides valuable additional information for assessment of dietary mineral intake.