An outdoor tap is one of the most useful additions to a home — for watering the garden, washing the car, filling paddling pools, or supplying a garden workshop. It is also one of the more straightforward plumbing additions, but there is a right way and a wrong way to fit one. A correctly installed outdoor tap protects your drinking water supply from contamination and survives British winters without bursting. A badly fitted one can do neither.
The Backflow Prevention Requirement
The most important — and most commonly skipped — element of an outdoor tap installation is a check valve (also called a double-check valve or backflow prevention device). An outdoor tap is considered a "fluid category 3" risk under Water Industry Act Regulations because a hosepipe or sprinkler left in a paddling pool, water butt, or garden bed can siphon contaminated water back into the mains supply if pressure drops. A double-check valve on the indoor connection prevents this.
"The installation of an outside tap must include a double check valve, fitted as close as practicable to the point of connection to the supply pipe. This is a requirement of the Water Supply (Water Fittings) Regulations 1999, not merely good practice."— GOV.UK — Water Supply (Water Fittings) Regulations 1999
What the Installation Involves
A standard outdoor tap installation involves: identifying a suitable point on the cold supply pipe indoors (under the kitchen sink is common); fitting a tee piece and isolation valve; fitting the double-check valve immediately after the isolation valve; running a pipe through the wall (core-drilled with a slight fall outward to allow drainage); and fitting the external tap body with a wall plate elbow. The external tap should be the bib-type with a loose key so it can be removed when not in use, or a separate indoor isolation valve should be easily accessible for winter shutdown.
Notifying Your Water Company
Under the Water Supply (Water Fittings) Regulations, a new outdoor tap installation is notifiable to your water supplier — not to building control. In practice, this means a plumber carrying out the work should notify the water supplier that a new fitting has been added. Many plumbers do this automatically; it is worth confirming that they will.
Winterising Your Outdoor Tap
Before the first hard frost, close the indoor isolation valve and open the outdoor tap to drain the pipe section that runs outside. If the installation has a draining mechanism (a "loose key" tap that can be backed off to drain the wall section), use it. Pipe lagging on the section of pipe inside a cold wall cavity provides additional protection. A burst outdoor tap section is a common, entirely preventable call-out in January and February.
"The section of pipe between the indoor isolation valve and the external tap fitting is the most vulnerable part of the installation in cold weather. Shutting the isolation valve and opening the tap to drain this section before winter costs nothing and prevents the most common outdoor tap failure."— Citizens Advice — Water Supply Problems
Repairing a Leaking Outdoor Tap
The most common outdoor tap faults are: a dripping spout (worn jumper valve washer — a standard tap washer repair); a leaking gland nut above the tap head (worn packing — can often be tightened or repacked); and a cracked body from a winter freeze. A cracked tap body requires replacing the whole fitting. Most standard bib taps take a ½ inch thread and replacement parts are widely available; older or unusual fittings can be harder to source and a plumber will advise.
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