Historically all the sewage and rainwater used to go into the nearest ditch. When the smell got bad the ditch became a pipe leading into a main river, though there was no treatment. Later all the pipes were run to treatment works called sewage farms. These were actual fields of turnips and cabbages. Although the treatment side has vastly improved we still have this combined surface water / sewage network in most cities. For maybe 50 years they’ve been building separate systems in new properties, but it’ll be a long time before all the old drains are sorted.
As far as I understand it. If you have combined sewerage in your street it’s permitted. If your street has separated foul/run off water pipes then it’s not allowed. otherwise if you get a huge storm then the foul system isn’t designed to handle that volume of water. It gets overwhelmed and the drain covers lift and mr poo and all his friends go for a nice float along the street. there’s a £4000 fine for putting foul water into run off drains.
If you have a look at your water bill, you may find you’re being charged for runoff disposal/processing anyway, so no prob.
