Joint water supply to outside garden tap?

beternal · Jun 3, 2025

Our kitchen is facing the garden and below the sink window on the outside wall is our garden tap.

There is a blue (washing machine-style?) tap under the sink and a mains tap behind one of the kickboards a bit further along.

I want to change the outside tap as it has seized up but cannot seem to turn the water off! I have tried the blue tap, and the mains tap behind the kickboard, and it still runs. This DOES turn off the kitchen tap and all water to the house. I have even gone down to the street and turned off the mains stopcock. This also turns off (as it would) the water to the house, but NOT the outside tap.

The weird thing is, that when I turn off the mains (inside and/or outside), the pressure to this outside tap drops, but does not shut off completely.

I have tried running it for a good half hour (maybe emptying radiators, boiler?... I don't know), but no, there's still water.

We are in a semi-detached, so could this one tap be fed from both sides?

Ideas, advice?

Rtplumb · Jun 3, 2025

beternal said:
Our kitchen is facing the garden and below the sink window on the outside wall is our garden tap.

There is a blue (washing machine-style?) tap under the sink and a mains tap behind one of the kickboards a bit further along.

I want to change the outside tap as it has seized up but cannot seem to turn the water off! I have tried the blue tap, and the mains tap behind the kickboard, and it still runs. This DOES turn off the kitchen tap and all water to the house. I have even gone down to the street and turned off the mains stopcock. This also turns off (as it would) the water to the house, but NOT the outside tap.

The weird thing is, that when I turn off the mains (inside and/or outside), the pressure to this outside tap drops, but does not shut off completely.

I have tried running it for a good half hour (maybe emptying radiators, boiler?... I don't know), but no, there's still water.

We are in a semi-detached, so could this one tap be fed from both sides?

Ideas, advice?

Hi beternal,

What you could do (if you're feeling brave) is to turn off the mains internal stop tap, open all the cold taps in the house including the outside one, and just change it while live. It's outside so no harm will be done. It might just stop running after a while anyway.

Hope this helps.

beternal · Jun 3, 2025

Rtplumb said:
Hi beternal,

What you could do (if you're feeling brave) is to turn off the mains internal stop tap, open all the cold taps in the house including the outside one, and just change it while live. It's outside so no harm will be done. It might just stop running after a while anyway.

Hope this helps.

I was considering this, but turning off the mains only reduces the water pressure to that tap by about 50%. This is what's confusing me... there must be two sources of water going to it.

My concern is that once I take the tap off, I'm committed if I do it 'live'. If for some reason I can't get it back on, or the thread is damaged, I'm in big trouble.

There is also a plastic outlet pipe JUST next to it. I'd rather not cut it if I don't have to, but it's a time constraint. If the water is off, I can remove and fit, and if the pipe is in the way, so be it... but if the water is live and then I find the pipe is in the way, it's rushed surgery, and then a tap that might not fit anyway.

I might end up doing this anyway though.

The real question was whether people had ideas about where the water is coming from!

Chuck · Jun 3, 2025

Ask your neighbour to turn off their supply at the same time you turn off yours, see what effect it has.

Are you sure the isolator(s) you are turning off are actually closing properly? When you close the stop-cock does the kitchen cold-tap stop working?

Do you have an unvented hot-water cylinder? If its non-return valve is faulty it could act as a big reservoir of water.

Do you have a water meter? If so, does the volume water needed to fill a bucket from the garden tap, e.g. 10 litres, match the readings on the meter?

IIRC, semi-detached houses in the UK built before WW2 could share a service pipe. I guess it's possible that when the supplies were separated someone connected the new supply to the wrong point and left a 'short-circuit' between the two halves of the house. I've not come across this myself but it's a theoretical possibility that my first suggestion above will prove or disprove.

william_1996 · Jun 12, 2025

beternal said:
Our kitchen is facing the garden and below the sink window on the outside wall is our garden tap.

There is a blue (washing machine-style?) tap under the sink and a mains tap behind one of the kickboards a bit further along.

I want to change the outside tap as it has seized up but cannot seem to turn the water off! I have tried the blue tap, and the mains tap behind the kickboard, and it still runs. This DOES turn off the kitchen tap and all water to the house. I have even gone down to the street and turned off the mains stopcock. This also turns off (as it would) the water to the house, but NOT the outside tap.

The weird thing is, that when I turn off the mains (inside and/or outside), the pressure to this outside tap drops, but does not shut off completely.

I have tried running it for a good half hour (maybe emptying radiators, boiler?... I don't know), but no, there's still water.

We are in a semi-detached, so could this one tap be fed from both sides?

Ideas, advice?

That’s a strange one!

If the outside tap still runs a bit even after shutting off your inside and street mains, there’s a chance it’s been plumbed into something unexpected maybe even tee’d off a shared supply or an old bypass line that was never properly isolated.
You mentioned a semi-detached is it possible the tap was originally part of a shared setup or even added later without following the main layout? I've seen some setups where an outside tap was oddly connected to a garden irrigation system or even taken off a loft cold water tank (though less common these days).

Might be worth tracing the pipework as best you can or getting someone in to help map it out could save you a headache later on!

Hope you get it sorted!