ARS | Publication request: The Mineral Content of U.S. Drinking and Municipal Water

Submitted to: National Nutrient Databank Conference
Publication Type: Abstract Only
Publication Acceptance Date: January 16, 2008
Publication Date: May 12, 2008
Citation: Pehrsson, P.R., Patterson, K.K., Perry, C. 2008. The mineral content of U.S. drinking and municipal water. 32nd National Nutrient Databank Conference, May 12-14, 2008, Ottawa, Ontario, Canada.

Technical Abstract: Objective: The mineral composition of tap water may contribute significant amounts of some minerals to dietary intake. The USDA’s Nutrient Data Laboratory (NDL) conducted a study of the mineral content of residential tap water, to generate new current data for the USDA National Nutrient Database. Sodium, potassium, calcium, magnesium, iron, copper, manganese, phosphorus, and zinc were determined in a nationally representative sampling of drinking water. Materials and Methods: The sampling method involved: serpentine ordering of the US population by census region, division, state and county; division of the population into 72 equal size zones; and random selection of one county per zone and two residences per county (144 locations). Chromy’s probability-proportional-to-size (population density), probability of minimum replacement method was used. Participants collected samples in HDPE bottles at two points in time (winter and spring, n=288) and provided information on water source (municipal, well), pipes and use of water softeners and treatments. Samples were analyzed by inductively coupled plasma atomic emission spectrometry; resulting data were analyzed using a mixed model approach. Results: Assuming two liters of tap water are consumed daily, only four minerals provided more than 1% of the U.S. Daily Value (DV): copper, 10%; calcium, 6%; magnesium, 5%; and sodium, 3%. Significant decreases in calcium were observed with chemical water softeners (mean 3.2 v. 2.0; median 2.73 v. 0.44 mg/100g), and between pickups for Mg and Ca (p<0.05). The variance of sodium was significantly different among regions (p<0.05); 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. Significance: These results, the first nationally representative dataset of mineral values for municipal drinking water, will provide valuable information for assessment of dietary mineral intake, including from water.