AMOUNT OF IRON REQUIRED TO RENDER WATER OBJECTIONABLE.
Three hundredths of a part in 100,000 of metallic iron very rarely precipitate or cause any trouble. Five hundredths occasionally precipitate, and this amount may be taken as about the allowable limit of iron in a satisfactory water. One tenth of a part is quite sure to precipitate and give rise to serious complaint. Two or three tenths make the water entirely unsuitable for laundry purposes, and are otherwise seriously objectionable, and will hardly be tolerated by a community. Under some conditions ground-waters carry as much as 1 part in 100,000 of iron, and such waters are hardly usable. In iron-removal plants an effluent containing less than 0.05 is regarded as satisfactory. One containing less than 0.02, as is the case with many plants, is all that can be desired. The percentage of removal is of no significance, but only the amount left in the effluent.