Iron can cause "red water" when its concentration exceeds what secondary maximum contaminant level?

The phenomenon of "red water" is typically associated with elevated levels of iron in drinking water. When the concentration of iron exceeds 0.30 mg/L, it can lead to aesthetic issues such as discoloration, manifesting as reddish or brownish water. This level is significant because it is considered the secondary maximum contaminant level (SMCL) set by regulatory agencies, aimed at minimizing nuisance conditions rather than health risks.

Levels above this threshold can cause staining of laundry and fixtures, which is a concern for consumers and can lead to complaints about water quality. Controlling iron concentrations within these limits is essential for maintaining acceptable water aesthetics and user satisfaction, even though iron is not a primary health concern. The specified level of 0.30 mg/L is intended to ensure that the water supplied does not detract from the public’s acceptance and trust in the water distribution system.