Today's question: Is urban runoff treated before being discharged into drinking water sources?
"Plain Talk" answer: Because of concerns about pollution, more and more communities are capturing and treating their stormwater before it reaches drinking water sources. One way is to hold the water in detention ponds so some of the sediment and associated pollutants settle out before it is discharged. A number of manufactured devices are also available to treat runoff, including catch-basin inserts that capture debris and filter out some pollutants, such as oil; hydrodynamic separators that remove pollutants from the water through filtration or other means; and underground storage units. Such practices are expensive and can treat only a portion of the runoff.
Some communities, especially older cities, have combined sewer systems (the sanitary sewer and the storm sewer are the same), so all water is routed to a wastewater treatment plant. As cities grow, however, the combined sewer systems become too small for all the water and can overflow during a heavy storm, releasing untreated sewage to the environment. As a result, many cities are working on creating a separate storm sewer system that will capture and treat the water that flows into the storm sewer before it's discharged.
For more information on this and many other water-related topics, check out "Plain Talk About Drinking Water" by Dr. James M. Symons.