250 mg/ I
15 color units
0.5 mg/ I Iron
6.5 - 8.5
Su I fate
Table 4-3. Recommended secondary MCL in drinking water.
(b) Laxative effect. Both sodium sulfate and magnesium sulfate are
well known laxatives. Calcium sulfate is much less active in this respect. As with taste,
the threshold for laxative effect varies considerably with the individual. Newcomers are
commonly affected, but one evidently becomes acclimated in a relatively short time.
When water is high in magnesium, a laxative effect occurs at lower sulfate
concentrations than when the cation is calcium, potassium, or sodium.
sulfates, cause noncarbonate hardness in water. Hardness is undesirable in that it
consumes soap, makes water less satisfactory for cooking, and produces scale in
(2) Copper. Copper is an essential and beneficial element in human
metabolism. In infants, a deficiency in copper results in nutritional anemia. Small
amounts are regarded as nontoxic, but large doses may cause vomiting. Prolonged
oral administration may result in Iiver damage. The recommended Iimit is based upon
the lower taste threshold.
(3) Foaming agents. These synthetic organic chemicals belong to a group
of chemicals known as anionic surfactants. These chemicals, whose action is the
reduction of surface tension, are the principal ingredients in 75 percent of the common
household detergents. Contamination of drinking water supplies with surfactants results
from their disposal, as household and industrial wastes, into sources of raw water.
They are appearing in supplies from both surface and ground waters. Concentrations
as low as 1 mg/l cause frothing and objectionable taste. Concentrations above 0.5 mg/l
are considered indicative of questionably, undesirable levels of waste water pollution.