Installing an Outside Tap — What's Involved
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →An outside tap must be fitted with a double check valve (or verifiable backflow preventer) to prevent contamination of the mains supply — this is a Water Regulations requirement. Failure to fit one can be an offence.
An outside tap is one of those additions that makes garden life considerably easier — whether you're watering plants, washing the car, or filling a paddling pool. Many homeowners assume it's a straightforward job, but there's a crucial legal requirement that often catches people out: Water Regulations mandate a double check valve to protect the mains supply from contamination. The good news is that a competent DIYer can usually manage this in a couple of hours, and it doesn't require specialist tools beyond a core drill bit and basic plumbing fittings. This guide walks through the planning, installation, and winter maintenance needed to get it right — and importantly, how to stay on the right side of the law. If you're not confident working with pipework or drilling through external walls, it's worth calling a qualified plumber to handle the job properly.
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Choose the location — ideally close to an internal water supply (usually the kitchen cold mains) to keep the run of pipe short and minimise drilling.
Turn off the cold water supply at the stopcock before making any connections to the pipework.
Drill through the external wall — a 32–40mm hole is typically needed to allow the pipe to pass through. Use a long core drill bit through brick.
Install the double check valve on the supply pipe before the tap — this is a legal requirement under the Water Supply (Water Fittings) Regulations 1999 to prevent backflow contaminating the mains.
Run 15mm copper or plastic push-fit pipe from the check valve through the wall to the tap position.
Fit the outside tap and bib tap backplate to the external wall. Connect the pipe using a compression or push-fit fitting.
Turn the water back on slowly and check all connections for leaks. Notify your water company within 5 working days of fitting an outside tap — required under water regulations.
For winter: always fit an isolation valve inside so you can drain the outside tap and prevent it freezing. Turn off and drain the tap each autumn.
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Frequently asked questions
Do I need building regulations approval to fit an outside tap?
Outside taps are generally considered minor works and don't require building control sign-off, but you must notify your water company within 5 working days of installation under Water Regulations. Always check with your local authority first, as some areas may have specific requirements.
Can I use plastic pipe instead of copper for an outside tap?
Yes, 15mm plastic push-fit pipe (like MDPE or polybutylene) works perfectly well and is often easier to install than copper. Make sure it's rated for external use and properly supported, especially where it passes through the wall.
What size hole do I need to drill through the external wall?
A 32–40mm hole is typically sufficient for 15mm pipework, depending on the pipe material and any protective ducting you plan to use. Use a long core drill bit rated for masonry; if you hit reinforced concrete or stone, consider hiring a professional with the right equipment.
Why does my outside tap freeze in winter and how do I stop it?
Water left in exposed pipework freezes in cold temperatures, blocking the tap and potentially bursting the pipe. Fit an internal isolation valve so you can shut off and fully drain the outside tap each autumn — a simple but essential step that saves costly repairs.
What's the difference between a double check valve and a single check valve?
A double check valve has two internal check mechanisms for greater protection against backflow and is the standard required by Water Regulations for outside taps. A single check valve offers less protection and may not meet current legislation, so always specify the double version.
Can I fit an outside tap myself or should I hire a plumber?
If you're comfortable with basic plumbing, drilling through walls, and understand the regulatory requirements, you can do it yourself in 2–3 hours. However, if you're unsure about any stage — particularly the double check valve installation or your water company's requirements — it's worth getting a qualified plumber to ensure it's compliant.