How to Install an Outside Tap: A UK Plumber's Guide

Installing an outside tap is one of the most popular summer plumbing jobs — and one of the most rewarding. Done properly, it gives you a permanent garden water supply for watering, car washing, and filling paddling pools without trailing hoses through the house.

This guide covers everything a plumber or confident DIYer needs to know: how to choose the right tap and fittings, where to break into the supply, the correct isolation setup, and how to comply with Water Regulations.

Do You Need Permission to Fit an Outside Tap?

In most cases, no planning permission is needed for a standard domestic outside tap. However, under the Water Supply (Water Fittings) Regulations 1999, you must notify your water company if the tap will be used for:

• Hosepipe use above domestic personal garden watering
• Supplying a pool or pond above certain volumes
• Commercial or trade use

For a standard domestic garden tap, notification requirements are minimal — but the installation must still comply. The critical requirement is fitting an appropriate non-return valve (NRV) or double-check valve (DCV) to prevent backflow, which could contaminate the mains supply. Most modern outside tap kits include this built in.

What You Need: Outside Tap Installation Kit

A basic outside tap installation uses:

• The tap itself — a brass outside tap or bib tap (usually 1/2" BSP)
• Isolation valve / service valve — to isolate the tap inside without draining down the system. A lever ball valve or isolating valve is best.
• Non-return valve — prevents backflow into the mains (may be built into the tap body)
• Backplate elbow — 15mm to 1/2" BSP, wall-mounted, gives a solid anchor for the tap
• 15mm copper pipe or MDPE pipe — to run from the cold supply to the outside wall
• Compression or push-fit fittings — compression fittings are most reliable outdoors where soldering is impractical
• Stop tap — if the supply branch doesn't already have one upstream (see stop taps)
• PTFE tape and jointing compound — for all BSP threaded connections (plumbing compounds and sealants)
• Pipe lagging — wrap any pipe in an unheated garage, roof void, or exposed run to protect from frost
• Core drill or hole saw — to pass the pipe through the wall (usually 25–35mm hole)

Step-by-Step: How to Install an Outside Tap

1. Find Your Cold Water Supply

Outside taps should always be connected to the cold mains supply (rising main), not to a storage tank or the hot supply. The rising main runs from the main stopcock (usually under the kitchen sink) vertically up through the house.

Choose a connection point as close as possible to where the tap will exit the wall — typically a kitchen or utility room cold supply. If the run is long (over 3m), use 22mm pipe to the point of use and reduce down to 15mm at the tap connection.

2. Isolate and Drain the Supply

Turn off the main stopcock. Open the cold kitchen tap to drain residual pressure. If you're working in a pressurised system with no cold water storage, this fully isolates your branch.

3. Break Into the Supply and Fit the Isolation Valve

Cut the cold supply pipe and fit a tee using compression fittings. Add an in-line isolating valve immediately after the tee on the new branch. This lets you turn off the outside tap supply independently — essential for winter draining and if the tap develops a fault.

Best practice: Use a full-bore lever ball valve rather than a screwdriver-slot service valve for garden taps. Ball valves give a clear visual open/shut indication and flow better when the tap is running a hose under pressure.

4. Run the Pipe to the Outside Wall

Run 15mm copper or MDPE pipe from the isolation valve to the exit point on the wall. Route it through existing duct or drill a 28mm hole through the masonry using a core drill. Use a grommet or exterior-grade sealant around the pipe where it passes through the wall.

Keep the pipe run as short as possible and slope it very slightly back towards the inside — this makes winter draining easier.

5. Fit the Backplate Elbow and Non-Return Valve

Outside the wall, fit a 15mm × 1/2" BSP backplate elbow to give the tap a solid fixing point. Use rawl plugs and screws into solid masonry.

If your tap does not include a built-in non-return valve, fit a double-check valve (DCV) inline in the supply before the tap. This is required under Water Regulations to prevent garden hose contamination from backflowing into the mains.

6. Connect and Test the Tap

Thread the tap into the backplate elbow using PTFE tape on the male thread — wrap 3–4 times clockwise when looking at the thread end. Do not over-tighten; hand-tight plus 1.5 turns with a spanner is sufficient for brass BSP.

Restore water to the supply. Check all compression joints and threaded connections for drips. Open the outside tap to purge air, then close it and verify the isolating valve downstream shuts off flow.

Frost Protection: Essential for UK Winters

Outside taps are one of the most common sources of burst pipes in UK winters. Protect your installation by:

• Draining down in October — close the indoor isolation valve and open the outside tap to drain the exposed run
• Insulating the pipe run — any pipe in an unheated space (garage, under a crawl deck, behind external cladding) should be fitted with foam pipe lagging
• Using a self-draining bib tap — some bib taps have a built-in drain valve that drains the external portion automatically when the indoor valve is closed

Troubleshooting Common Outside Tap Problems

Materials to Collect from APM

Everything you need for a standard outside tap installation is available for same-day collection from APM Electricals in Acton, West London:

• Lever ball valves — 15mm full-bore, for isolation
• Compression fittings — tees, elbows, stop-ends
• Stop taps — for new supply branches
• MDPE pipe and fittings — blue mains water pipe where a long external run is needed
• PTFE tape and jointing compound
• Flexible hoses — for tight connection points

Trade counter open Monday–Saturday. Call ahead on 020 8702 8080 to confirm stock on specific tap bodies or backplate elbows.

Products Available from APM Plumbing & Electrical

Key outside tap kits and garden tap components available for trade collection or delivery: