Odd, low mains pressure.

7 Mar 2021
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United Kingdom
My mains pressure has always been a steady 1.5bar, About a week ago it reduced to about 0.2 The inlet stop cock and pipes make a hissing sound. Pic 1 shows water main A, but there is also an odd thing. If I put my ear to toilet drain downpipe B, there is a clear sound of running water in it. Here's what I've checked. When the stopcock is off, both sounds remain. When the stopcock in road is off, both sounds stop. Mains supply in the road has been checked by TW and aok. There is nothing going down the toilet drain (condensate, toilet leak etc).

So it's, likely I have a supply leak on my side? I cannot see any external signs of leak. Is it possible that beneath my slab the water main pipe runs into and through the toilet drain. I'm sure I must have a supply leak but cannot understand why the runnung noise is coming from the toilet drain?


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Does seem like you have a supply leak on your side. I guess you haven't got a meter;) Have you got a manhole you can lift and see the WC flow ? It could be noise transmission through the earth from main to soilpipe. Or water flowing into the drain through cracks.
I'm still on unmetered or this would probably be costing me. There's a drain about 10m away but can't hear any noise at all from it? Do you know if a plumber could locate a leak or would i have to get a specialist?
It looks like you have a suspended wooden floor around where the incoming mains emerges. Have a look below the floor for any signs of damp, or any further noises.
I assume that soil pipe will lead to an outside culvert with a manhole cover. With the street mains on and the house mains off you said there is still a sound of running water. Can you detect it in the manhole?

Screwfix, and online retailers often have quite cheap boroscopes suitable for looking into tight and dark areas (no smutty remarks required here!).

PS to drop from 1.5 to 0.2 bar there will probably be a large leak somewhere.
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Pic is not very good but the wooden "clicklock" floor is just laid on the concrete slab (with underlay). The concrete is exposed around the water main and drain area and there is no sign of any moisture except for a small amount damp at ther back of the drain. I have listened (using a rod) both inside and outside the house and can only here the hissing sound in the pipes and the running water noise in the drain. It's as if the main is leaking directly into the drain but I don't know if that's possible. Thanks for the advice on the boroscope, I'll have a look into that.

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