Wastewater is about what percentage of water?

• A. 99.5 - 99.8
• B. 99.0 - 99.2
• C. 99.75 - 99.85
• D. 99.8 - 99.9

Answer: (D)

Wastewater is composed mostly of water; the solids and contaminants are a small fraction. In typical municipal wastewater, the water makes up about 99.8 to 99.9 percent of the mixture, with the remainder being suspended and dissolved solids, organic matter, and microbes. This very high water content is why treatment plants handle large volumes of water while removing the relatively small amount of pollutants. The near-total water content means the fraction of solids is only about 0.1 to 0.2 percent, so the range 99.8–99.9 percent best reflects the reality.