Outside Tap Installation Guide
An outside tap is a quick job that carries a real compliance requirement: a garden tap is a fluid category 3 risk, so it needs backflow protection — and it needs protecting from frost. Get both right and it lasts for years.
Fitting an outside tap is one of the more popular small plumbing jobs, but it is not simply a matter of teeing off the cold main and running a tap through the wall. A garden tap can be connected to a hose lying in a puddle or a chemical sprayer, so under the Water Supply (Water Fittings) Regulations 1999 it is treated as a fluid category 3 backflow risk and must be protected accordingly.
This guide covers the compliant way to do it: taking the connection off the rising main, providing the required double-check valve backflow protection, giving the tap its own internal isolation and a means to drain down for frost, and finishing the pipework neatly through the wall. It is written to leave the installation both watertight and Water-Regulations compliant.
Key takeaways
- A garden tap is a fluid category 3 backflow risk, so it requires a double-check valve (or an approved equivalent) under the Water Regulations.
- Take the supply from the rising main after the internal stopcock, and fit a dedicated isolation valve so the tap can be shut off from inside.
- Provide a means to drain the external pipe down over winter, or use a self-draining/frost-proof design, to prevent freeze damage.
- Sleeve and seal the pipe where it passes through the wall, and support the tap so it doesn't work loose in use.
- Notify or check any requirements with the water undertaker where applicable, and keep the whole installation to WRAS-recognised fittings.
Where to take the supply and isolation
Connect the outside tap to the rising (cold mains) main, downstream of the property's main internal stopcock so the whole house isn't disturbed when the tap is worked on. Fit a dedicated isolation or lever valve on the branch inside so the outside tap can be turned off independently — essential for winter shut-off and for any future repair.
Keep the internal pipe run tidy and properly clipped, and site the through-wall penetration where the external tap will be at a sensible working height and won't be fouled by paths or planting. Plan the route before you cut anything.
Backflow protection — the compliance point
This is the part that makes the job compliant. Because a hose connected to a garden tap can be submerged in contaminated water — a water butt, a pond, a bucket of weedkiller — the tap is a fluid category 3 risk. The Water Supply (Water Fittings) Regulations 1999 require backflow protection appropriate to that category, which for a garden tap means a double-check valve (DCV), or a purpose-made tap with integral check valve protection to the same standard.
Fit the double-check valve in the supply to the tap, on the warm side of the wall where it will not freeze, using WRAS-recognised fittings. Many outside-tap kits include an integral DCV; if you build the assembly yourself, the check valve protection is not optional — it is the reason the installation meets the regulations.
The double-check valve is mandatory, not optional
A garden tap is category 3 by default. Leaving off the double-check valve is a Water Regulations breach, not a cosmetic shortcut — build it in and use recognised fittings.
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Protecting against frost
An external tap and the pipe feeding it are exposed to freezing, and a burst behind the wall is a far bigger job than the original install. Provide a way to isolate and drain the external section over winter: the internal isolation valve plus a drain-off point, or a frost-proof/self-draining tap that empties the vulnerable outdoor length automatically when closed.
Insulate exposed pipework, keep the length of unprotected external pipe to a minimum, and advise the customer to shut off and drain the tap before the first frosts. A little foresight here prevents the classic spring call-out to a split pipe.
Drain it down before winter
The commonest outside-tap failure is a frozen, split pipe. Fit an internal isolator and drain-off, or a self-draining tap, and tell the customer to shut it off for winter.
Through the wall, finishing and pricing
Drill the through-wall hole with a slight outward fall so any water drains away from the building, sleeve the pipe where it passes through the masonry, and seal the penetration against draughts and driving rain. Fix the tap or wall plate securely so the tap doesn't rack the pipe every time a hose is fitted, and make the external joint on a compression or soldered fitting kept clear of the wall face for future access.
For pricing, an outside tap is a small but skilled job with a genuine compliance element — price it to include the backflow fitting, isolation, drain-down provision and making good, not just the tap and an hour's labour.
Quote and certify in one place
Build the outside-tap quote in TradePlanr with the backflow and drain-down work as visible lines, then record the WRAS compliance and hand the customer a proper certificate before you leave.
From guidance to action
Frequently asked questions
Does an outside tap legally need a double-check valve?
Yes. A garden tap is classed as a fluid category 3 backflow risk because a hose can be submerged in contaminated water. The Water Supply (Water Fittings) Regulations 1999 require appropriate backflow protection, which for a garden tap means a double-check valve or a tap with equivalent integral check-valve protection.
Where should the double-check valve go?
Fit it in the supply to the tap, on the internal (warm) side of the wall so it is not exposed to frost, using WRAS-recognised fittings. Many outside-tap kits include an integral double-check valve for exactly this purpose.
How do I stop an outside tap freezing?
Provide a way to isolate and drain the external section — an internal isolation valve plus a drain-off point — or fit a frost-proof, self-draining tap. Insulate exposed pipe, minimise the unprotected external run, and shut the tap off and drain it before winter.
Related guides
The Water Regulations 1999 Explained
Fluid categories, backflow prevention and notification — the Water Fittings Regs in plain terms.
Water Hammer: Causes and Fixes
Why pipes bang, the difference between water hammer and expansion noise, and how to diagnose and fix it.
Bathroom Installation Guide
Install a bathroom start to finish — planning, first-fix, water-regulations compliance, second-fix, testing and pricing the job in stages.
