Naturally occurring minerals, such as calcium, sulfate, and magnesium, are typically present in most conventional water supplies at concentrations greater than 1 mg/liter. They are regulated according to secondary U.S. drinking water standards, based primarily on their aesthetic effects. The concentrations of these chemical species and of nitrogen-containing compounds and other inorganic salts increase as the water is used and then collected as wastewater. However, the potential hazards they pose to downstream consumers remain manageable because these minerals and salts can be accurately quantified in water, and well-established treatment processes can usually reduce their concentrations to levels complying with national drinking water standards or recommended limits.

Levels of phosphate and nitrogen, two other chemicals commonly found in wastewater, are often monitored at treatment plants because of their potential effects on the ecology of receiving waters. Phosphorus can be efficiently removed from wastewater by chemical precipitation or various biological processes, and nitrogen can be removed by biological