The world is running out of fresh water - lakes are drying up, rivers don't reach the ocean, streams and lakes are polluted and the built environment encourages runoff, as does degraded soil.
Apart from erosion, runoff prevents water from getting back into the ground where it belongs. Let's look at an example close to home - Corning's waste water treatment plant. If I remember correctly, the plant handles about 3 million gallons of water on an average day. This can increase to 6 million if there is heavy rain.
What happens is this. Corning draws s much water as it needs from the aquifer, contaminates in various ways (mostly through toilets), passes it briefly through the WWTP, and discharges the "clean" water into the Chemung River. The Chemung joins the Susquehanna which eventually empties into Chesapeake Bay. The bay area has been working very hard to clean up their waters and they have managed to put in place some restrictions on the levels of contamination occurring upstream. As a result, Corning will have to spend some 2.5 million dollars over the next few years to remove both bacteria and phosphorus from the water before it can be discharged into the river.
Now I may have some details wrong, but I have not been allowed to see the WWTP and get answers to my questions. There is - it seems to me - a very simple solution: don't discharge the water into the river! Put it back in the ground instead.
This can be done in two ways. First, increase permeability of all surfaces so that storm water is absorbed and doesn't find its way to the WWTP, and secondly, divert the treated water into a wetland, natural or constructed. That way the water will slowly filter back down to the aquifer. Please note the word "filter" - soil is a great filter.