Does water entering storm drains get sanitized before it hits the river?

Lots of gutters (but not all of them) in our older neighborhoods are labeled “Drains to waterway (or to river).” Is it still true that some of the gutter water goes directly to the river and doesn’t join the sewage system? It would seem that modern environmental runoff would need to be sanitized like sewage.

Stormwater does generally go to the river rather than the treatment plant where household wastewater goes. But the path is indirect, and on the way, some cleaning does take place.

By way of illustrating that long and winding road, imagine a burst of rain falling on a Greater Downtown parking lot and then heading toward one of the city’s 16,000ish storm sewer inlets. There it begins a trip through manholes, pipes, and culverts (720 miles combined in the city alone), arroyos, drainage ponds (116 in the city), and finally one of 14 city pumps that will push it toward the Rio Grande.

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