An experimental bottled water study assessed the effect on blood pressure of lowering Na concentration in the water of some of the high sodium community fourth graders. For three months, trios of children matched by sex, school, and baseline BP each used different water for all cooking and drinking purposes, with BP monitored bi-weekly. Pupils were randomly allocated to the three water conditions: high sodium water bottled from their own community distribution system, low sodium water bottled from the distribution system of the comparison community with sodium added to the level of the high sodium community water and low sodium water bottled from the distribution system of the low sodium community but with no sodium added. The results indicate that BP levels among the girls but not boys on the low sodium water exhibited marked decreases in BP over the test period when compared to the other two groups.