Water sodium and blood pressure in rural school children. 
Blood pressures were measured in 326 boys and 309 girls, 12 to 14 yr of age, who attended schools in six rural towns with water sodium levels ranging from 1.46 to 9.69 mmol/L. Although there were significant differences between mean blood pressure levels in children living in the six towns, they did not appear to result from differences in water sodium levels.  Children who lived on farms and who drank low-sodium rain water did not have lower blood pressures than children who lived in the towns.  The estimated intake of sodium from drinking water in the towns varied between 1.5 and 11.6 mmol/day and represented between 1.2% and 10.4% of the estimated daily sodium intake.  No effect of water sodium level on urinary sodium excretion was found.  Blood pressure levels showed significant positive relationships with pulse rate, body height and weight, Quetelet's index, mid-upperarm circumference, and triceps skinfold thickness.  Diastolic blood pressures in girls were inversely related to the measure of physical activity.  Control of these variables, where relevant, by covariance analysis did not uncover any relationship between water sodium level and blood pressure.