What is it?
The plumbing is everything behind and below the sink that brings water in and takes it away. Two supplies rise up to the sink area, a hot and a cold, usually in copper pipe, and each has an isolation valve so it can be shut off on its own for work on the tap or an appliance. The main stopcock, which turns off the whole cold supply to the house, normally sits on the cold pipe under the kitchen sink.
From the supplies, flexible hoses feed the tap with hot and cold, and a separate cold feed runs to the dishwasher, which heats its own water and so needs no hot supply. On the waste side, a white plastic pipe carries water away through a trap, the U bend that holds a plug of water to stop drain smells coming back up, and the dishwasher drains into that same trap. The sink's own overflow ties in here too, guarding against the bowl overfilling.
- 1Socket / Switch cutouts
- 2Hot water supply
- 3Cold water supply
- 4Stopcock
- 5Waste Pipes
What does it do?
Bringing water to the sink and appliances
Two supplies feed the tap and any appliances, hot and cold to the tap and a cold feed to the dishwasher. Each supply has an isolation valve, so a single fitting can be shut off without turning off the rest.
Taking waste water away
The waste pipe carries used water from the sink and the dishwasher down to the drain, with the trap holding a plug of water that keeps drain smells out of the kitchen.
Letting you shut things off safely
The isolation valves and the main stopcock mean the supply can be turned off quickly, either the whole house at the stopcock or a single fitting at its valve, which makes maintenance and emergencies far easier.
Where is it used?
The hub of kitchen plumbing, where the supplies, valves, stopcock, tap hoses, waste and appliance connections all come together inside the sink base unit.
Short branches off the supply and waste serve the dishwasher and washing machine, each with its own valve and a drain connection.
Where a sink or appliance sits away from the wall, the supply and waste are run through the floor or a services void to reach it.
Types
Kitchen plumbing can be put together in a few ways, and the choice is mostly about the pipe material and how the joints are made. Most kitchens use a mix of these.
Copper pipe
The traditional supply pipe, rigid and long lasting, joined by soldering or with compression fittings. It is neat and robust, but it takes more skill, and soldering needs a flame.
Plastic push fit
Flexible plastic pipe, such as Speedfit or Hep2O, joined by pushing it into a fitting that grips and seals it. Fast, with no tools or flame needed, and easy to alter later, which is why it is common on modern jobs.
Compression joints
Fittings that seal onto copper or plastic pipe by tightening a nut and olive, with no heat needed. Handy for connecting valves and for any joint that might need undoing later.
Flexible connectors
Braided flexible hoses that link the rigid supply to the tap tails and to appliances. They take up the awkward angles under a sink and make the final connection quick.
Waste pipe and traps
The white plastic side of the system, in push fit or solvent weld, carrying waste away through a trap that holds the water seal. Appliance drains tee into it.
Typical sizes
The common kitchen sizes are set by standard pipe and waste dimensions.
| Part | Typical size |
|---|---|
| Hot and cold supply pipe | 15 mm |
| Tap connection thread | half inch |
| Sink waste pipe | 40 mm |
| Trap water seal | around 75 mm |
| Appliance drain spigot | fits standard appliance hose |
How to specify
Kitchen plumbing is usually set out by the plumber to suit the layout, but the key choices are the pipe system, where the isolation points go, and how the appliances connect.
Pipe system and route
Choose the pipe material and jointing, copper or plastic push fit, and plan the route for the hot and cold supplies and the waste to reach the sink and appliances, keeping the runs short and accessible.Valves and isolation
Fit an isolation valve on each supply so the tap and each appliance can be shut off on its own, and confirm the stopcock position on the cold under the sink. Put them where they can actually be reached.Appliance and waste connections
Set the cold feed and drain connection for the dishwasher and any washing machine, tee the appliance drains into the sink trap, and make sure the waste falls correctly to the drain with the trap keeping its water seal.
Other considerations
Interacting elements
The plumbing connects the sink and its appliances to the building's water and drainage.
- Sink is served by the plumbing, which takes its waste through the trap and overflow.
- Tap is fed by the hot and cold supplies through flexible connectors.
- Dishwasher takes a cold feed and drains into the sink trap.
- Sink base unit houses all the plumbing beneath the sink.
- Worktop and splashback the tap and its connections pass up through or behind these.
- Washing machine where present, connects to supply and waste the same way as the dishwasher.
Popular manufacturers
McAlpine
A British manufacturer since 1907 and the market leader in traps, waste pipe and appliance connections, the plastic side of kitchen plumbing. WRAS certified and made in the UK, with a huge range of traps and dishwasher and washing machine connectors.
John Guest Speedfit
The British inventor of the plastic push fit system, making push fit pipe, fittings, isolation and service valves and flexible tap connectors. Tool free and flame free to fit, with a long guarantee and WRAS approval.
Pegler Yorkshire
A long established British name, now part of Aalberts, behind Yorkshire copper solder fittings and Pegler valves and stopcocks. A traditional choice for copper supply work and for isolation valves.