An outside tap must have a double check valve to prevent backflow into the drinking water supply – that is a requirement of the Water Supply (Water Fittings) Regulations, not an optional extra. It also needs an internal isolating valve and drain point so it can be shut off and emptied before winter.
The regulations bit, briefly
An outside tap is a point where a hosepipe can be connected. A hosepipe can sit in a water butt, a pond, a bucket of weedkiller or a paddling pool, and if the mains pressure drops for any reason – a burst in the street, the water company working on the main – water can be siphoned backwards out of that container and into the pipework of your house and potentially your neighbours’.
This is why the Water Supply (Water Fittings) Regulations require backflow protection on an outside tap. In practice that means a double check valve, fitted on the supply to the tap. It is a small brass fitting and it costs very little. A tap fitted without one is not compliant, and it is not a technicality – contaminated water going back into a drinking water main is exactly the scenario the regulations exist to prevent.
It is worth knowing whether it has a check valve. Many older ones do not, and many DIY installations do not. It can usually be added without much difficulty at the internal end of the run.
What a properly installed outside tap has
- A double check valve on the supply, as above.
- An internal isolating valve, so the tap can be shut off from inside without turning the whole house off.
- A drain point or a drain-down facility, so the external section can be emptied before winter. Without this, frost protection relies entirely on hoping.
- A properly sealed wall penetration, sleeved and made good on both faces. A hole drilled through a cavity wall and left open is a route for water and cold into the cavity.
- A sensible route. The shortest practical run of exposed pipe, ideally taken from a heated part of the house rather than a long cold run through an unheated garage or crawl space.
- A frost-resistant tap where the position warrants it, or insulation and a cover as a minimum.
Getting the position right at the start matters more than it sounds. The convenient wall internally is often the wrong wall externally – too far from where you actually use a hose, above a path where drips freeze, or on a north-facing elevation that never sees sun. It is worth two minutes of thought before anybody drills.
Frost, which is the whole problem
Water expands when it freezes and copper does not. A short section of exposed pipe with water standing in it on a hard Norfolk frost is a burst waiting for a thaw – and the burst does not usually show itself while it is frozen. It shows itself when everything warms up, often when nobody is home, and by then it is running into the wall.
The answer is straightforward and it takes thirty seconds each autumn: turn the internal isolation valve off, open the outside tap, and let the external section drain. Leave the outside tap open over winter so any residual water has somewhere to expand into. Turn it back on in spring.
This only works if there is an internal isolating valve and a way for the water to drain out. That is why those two items are not optional extras on the installation, and it is why an outside tap teed straight off a pipe with no isolation is an installation that will eventually cost somebody a ceiling.
Common jobs on existing taps
| Problem | Cause |
|---|---|
| Tap drips continuously | Worn washer or seat – a standard bib tap is a simple repair |
| Tap will not shut off at all | Seat damaged, often by grit or by being over-tightened when stiff |
| No water from the tap | Internal isolation left off, or the pipe has frozen – or burst, which you will discover on the thaw |
| Water appearing inside the wall in spring | A burst in the exposed section from the winter, only now showing |
| Tap turns but the whole assembly moves | Pipe not properly clipped inside, or the wall plate has pulled out. Worth fixing before it fractures the pipe |
| Poor flow | A restricted check valve, or a 15mm run teed off with a long thin length of something narrower |
Want one fitted before summer, or the existing one made safe for winter? It is a short job.
Questions we get asked about this
Do I need permission to fit an outside tap?
No permission, but the installation must comply with the water fittings regulations – which in practice means backflow protection. Some water companies ask to be notified of certain works; the double check valve is the substantive requirement.
Will an outside tap increase my water bill?
If you are on a meter, you pay for what you use through it, and garden watering adds up quickly. If you are unmetered it makes no difference to the bill. Either way a water butt fed from a downpipe is cheaper than a tap for most garden use.
Can you fit one where there is no convenient internal pipe?
Usually, though it becomes a longer job because the supply has to be run to the point. It is worth discussing the position rather than defaulting to wherever the pipework happens to be – the tap is going to be there for twenty years.
My outside tap froze and now it leaks. What happened?
The water in it expanded as it froze and split something – the tap body, the pipe, or a fitting. It needs the damaged section replacing, and it is worth adding isolation and a drain point at the same time so it does not happen again.
Should I lag the outside tap?
An insulated cover helps and costs almost nothing, but it is second best. Draining the section down each autumn is what actually prevents a burst, because there is then no water in it to freeze.
Can you fit a tap for a hot outside supply?
It is possible but it is rarely worth it – long runs of hot pipe to an external point lose most of their heat and create a legionella consideration on any dead leg. For most purposes there are better answers, and we will talk it through.
Regulations and standards referenced on this page
- The Water Supply (Water Fittings) Regulations 1999 (SI 1999/1148) — UK Statute Law Database
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