In an earlier contribution to this discussion,
S lo wrote:

Is it OK to reroute 3/4 of my roof's rain water down the foul water
pipe instead of down the surface water pipe?

My top floor flat has a dual water drainage system - FW and SW.
It has a double roof with a valley gutter between them, and two
gutters at the front and rear behind parapets.
Rain water from the centre valley and front gutters goes down
drainpipes inside my flat to the rear gutter and then it all goes
through the parapet down to ground at the back of the building.

The pipes are enclosed in massive plasterboard box sections running
the length of the flat and are not only taking up lots of space, but
develop leaks occasionally. When this happens, it's a real task to
open them up, repair the leaks and then replaster and paint them.

The SW pipe goes right next to the FW pipe at the centre valley, and
draining the SW from centre and front roof planes into the FW would
mean I could get rid of half of the pipe.

I know it's a mortal sin to connect FW to a SW drain, but how about
the other way around?
Cheers.

Many older properties have only one combined drainage system for FW and SW.
The idea of separating them for newer properties is that it cuts down on the
sewage treatment works capacity required - because SW can go straight into a
river without needing to be treated.

If you put SW into a FW system, it will get treated unnecessarily - but that
is about all. Some water boards give a discount on your water rates if your
surface water *doesn't* go into the FW system. If you currently get this
discount, you'll no longer qualify for it if you do what you propose - and
if the water board finds out! You're unlikely to end up in prison - for this
at any rate! g?
--
Cheers,
Set Square
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