How many sewage works are there in London and which rivers and waterways are they based close to?

There are 7 sewage treatment works in London all managed by Thames Water.

Sewage Treatment Works discharging into the Tidal Thames:

Hogsmill sewage treatment works discharges into the Hogsmill river with a small flow being pumped to the Beverley Brook.

Deephams sewage treatment works discharges into the Salmons Brook (and then the Lower Lea).