One increasingly common ...

One increasingly common supply is secondary treated municipal wastewater (gray water), but other supplies such as deep groundwater and seawater may be options as well. These supplies often contain some impurities in much higher concentration than in fresh water. For gray water, ammonia, phosphorus, and organic compounds are notable examples. Deep aquifer water can have an exceptionally high dissolved solids concentration, with chloride, sulfate, alkalinity, sodium, calcium, and other ions contributing to the total.