A couple of days ago there was some work being done on the drains in a road, which I'm pretty sure was sewage works. There was alot of water running down the road which looked clean so I assumed it was just overflow or whatever, anyhow I drove through this water, it wasn't deep or anything infact it just looked like it had been raining quite hard in one place. I thought nothing of it at the time but now if I have my heaters on so they're taking air from outside, you can faintly smell the same sewerage smell that was around on the night where I drove past it. I'm guessing that the water WASN'T as clean as it looked and has splashed up the underside of the car near to where the air vent is (wherever the fuck that is?). The question is, what do I do to stop it other than turning the heating on to re-circulate?