How do I fit an outside tap?

Mechanically this is a straightforward job. The parts that need care are the regulations, the drilling, and making sure the whole thing can be isolated and drained before the first frost.

Safety

What you'll need

• An outside tap kit with a wall plate and double check valve
• An isolating valve and a tee for the internal pipework
• A pipe and cable detector
• A long masonry bit of the right diameter
• Exterior-grade sealant

Step by step

1. Check the regulations apply to you.An outside tap must have backflow protection to at least fluid category 3, which in practice means a double check valve. Water companies expect to be notified of a new outside tap; some make a small charge.
2. Choose the supply point.A cold mains pipe with easy access — often under the kitchen sink or in a utility room. It must be mains cold, not a supply fed from a storage tank.
3. Plan the internal fittings in order.From the tee: an isolating valve, then a drain-off or a means of draining, then the double check valve, then through the wall to the tap. Getting them in this order is what makes winter draining possible.
4. Scan the wall before drilling.Use a detector on both faces. Look at what is on the other side and directly above and below — sockets, switches, meters and boiler flues all indicate services in the wall.
5. Drill on a slight downward slope to the outside.So any water in the hole runs out rather than in. Drill from inside outwards, and start the last part from outside to avoid blowing out the render.
6. Fit the wall plate securely.The plate carries the load of a hose being pulled on. Fix it into masonry with proper plugs, not into render alone.
7. Make up the pipe run.Compression or push-fit fittings are both fine inside. Use PTFE tape on the tap's threaded connection into the wall plate.
8. Cut into the mains pipe with the water off.Close the stopcock, open the lowest tap in the house to drain the pressure, and have towels ready. Cut with a pipe slice for a square end.
9. Seal the hole through the wall.Exterior-grade sealant around the pipe on both faces, sloped to shed water outside. An unsealed hole is a draught and a damp path.
10. Lag the pipe where it passes through.The section in the wall and any run in an unheated space needs insulating. This is where outside tap supplies freeze and split.
11. Test thoroughly.Restore the water slowly, check every joint by hand, and run the tap hard. Then check the internal joints again an hour later.
12. Notify the water company.Most require notification of a new outside tap. Check your supplier's process; it is usually a simple online form.

Tips

• Fit the isolating valve inside and upstream of everything else. It is what lets you drain the tap each autumn.
• A self-cutting tap connector avoids draining the house down, but a proper tee and isolating valve is a much better long-term job.
• Drill the wall in stages, checking with a detector as you go if the wall is thick.

Common mistakes

• Fitting an outside tap with no double check valve — A hose left in a water butt, a pond or a bucket of weedkiller can siphon back into the house supply and into the public main. Backflow protection is a legal requirement for this reason.
• Taking the supply from a tank-fed cold pipe — A gravity supply gives poor pressure at an outside tap, and stored water is not suitable for drinking-quality outlets. It has to come off the mains cold.

If it doesn't work

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