I'm involved in local housing development and neighbourhood plans. And this question bothers me. How do we deal with, and keep separate:- - Run off from fields and agricultural land - Run off from roads - Run off from roofs - Grey water from household washing and appliances (showers, baths, clothes washing, dish washing) - Foul water from sewage systems Because each one needs it's own dedicated processing. A few SUDS and a big sewage pipe is not enough. https://www.theguardian.com/environment/2023/oct/05/potentially-toxic-road-runoff-outfalls-polluting-england-rivers