Uh, we already have that. City sewer rate here is based on winter average water consumption (so at least we don't have to pay extra for water used for irrigation). We also have a separate fee based loosely on square footage, for "storm water treatment" (i.e. a rain tax), though the storm water flows through a series of open ditches into a lake with no treatment other than filtering through natural vegetation. But it is quality runoff. Otters, not seen around here in ages, have actually taken up residence in the system as of last year. The ditched stolen bikes and shopping carts don't seem to bother them. Our company's heavy equipment dealership is right next to one of the main canals. We keep booms around all the storm drains to catch small amounts of oil that could get in there, so it goes in reasonably clean (and as you can imagine it is watched very closely and any sheen detected downstream from us gets us a visit from the city). But the biggest water polluter in this area is the government. The county fairgrounds has repeatedly washed heaps of nitrate laden manure into the system. Causes a big stink (so to speak) each time it happens. So now their drainage goes to the sewer system, and you know who gets to pay for that.