30 REPORT OF INVESTIGATIONS NO. 50
Unpolluted water rarely contains excessive concentrations of the above toxic substances. In highly industrialized areas, objectionable amounts of toxic substances are sometimes found in water. Two samples, one from the St. Johns River at low flow and the other from a typical Orlando supply well, were analyzed for minor elements. The cadmium, chromium and lead concentrations were less than .0014 ppm.
The U. S. Public Health Service's standards for fluoride in drinking water are based on climatic conditions, because children drink more water in warmer climates and, consequently, consume more fluoride. Table 5 lists the drinking water standards for fluoride concentration. Where fluoride occurs naturally in water, it should not exceed the upper limit in table 5. Where fluoridation is practiced by water treatment plants, the concentration should be held between the lower and upper limits. The U. S. Public Health Service states that the presence of fluoride concentrations more than twice the optimum values in table 5 constitutes grounds for rejection of the supply. The yearly normal maximum daily temperature in Orange County is 80.90 F; therefore, the optimum amount of fluoride in drinking water is 0.7 ppm and the concentration should not be below 0.6 ppm or above 0.8 ppm. Fluoride concentrations in Orange County water are usually less than 0.8 ppm and often less than 0.4 ppm.
AGRICULTURAL USE
The primary non-domestic uses of water on the farm are for livestock consumption and for irrigation. The quality standards of
TABLE 5. DRINKING WATER STANDARDS FOR FLUORIDE CONCENTRATION.
Yearly normal maximum Recommended fluoride control
daily temperatures OF limits in ppm
Lower Optimum Upper
50.0 53.7 0.9 1.2 1.7 53.8 58.3 0.8 1.1 1.5 58.4 63.8 0.8 1.0 1.3 63.9 70.6 0.7 0.9 1.2 70.7 79.2 0.7 0.8 1.0 79.3 90.5 0.6 0.7 0.8