I live close to one of the tributaries that is significantly affected by the sewage issues in London at the moment, not far from the Three Mills area. I've looked at flats around there and they are a good 15-20% cheaper than I'd expect... with the main caveat being that much of the area kinda smells. I would expect many of them to increase in value once Tideway comes online and that area smells less.

I also walk along the Jubilee Greenway in East London quite a lot, and much of that is built on top of the old above-ground sewer pipes that lead down to the old Bazalgette sewage pumping station in Abbey Mills. Hopefully once those pipes are decommissioned the Jubilee Greenway should be much nicer to walk along!

https://en.wikipedia.org/wiki/Abbey_Mills_Pumping_Station

I suppose if the sewage pipe isn't there it would have a dramatic affect of reducing your home value :)