Renovating a London kitchen: the plumbing decisions you'll face

The plumbing in a kitchen renovation is mostly invisible by the end. But every decision you make about it locks in your hot water flow, your dishwasher position, and your worktop layout for the next 15 years. Here are the choices that matter most, with honest pros and cons.

Sink position

The single biggest decision. Move the sink even one metre and you affect:

• Hot and cold supply runs (need to be re-routed under the floor or through walls)
• Waste pipework (must drop towards the soil stack at 1:40 to 1:80 fall)
• Worktop layout and cutting
• Whether the dishwasher fits on either side of it

In a Victorian London terrace where the soil stack is at the back of the house, the sink usually wants to be on or near that wall. Moving it to a kitchen island in the middle of the room means a waste pipe running across the room (under the floor) to reach the stack. Possible but adds £1,500 to £3,500 to the plumbing cost depending on floor structure.

Honest advice: keep the sink near the existing waste position unless you have a strong reason to move it. The work involved is not worth the small change in layout.

Single bowl vs double bowl vs Belfast

Three main types:

• Single bowl (modern): large undermount sink, one big space. Best for washing big pans. Standard for new builds.
• Double bowl: two separate spaces. Useful if you wash large amounts by hand. Increasingly rare with dishwashers as standard.
• Belfast (apron front): large white ceramic sink that protrudes from the worktop. Heritage style, popular in period kitchens.

Plumbing implications:

• Single bowl: standard waste, no special considerations
• Double bowl: needs two waste connections joining into one trap (slightly more pipework)
• Belfast: heavier, requires reinforced cabinet underneath, often shorter cabinet height to accommodate the sink height

For a typical London kitchen, I see single bowl most often. Belfast is having a moment in stone or marble worktops, but factor in the extra cabinet build cost.

Tap type

Your kitchen tap is the part you use 30 times a day for the next decade. Worth choosing well.

Standard mixer (£60 to £200)

A swivel-spout mixer with hot and cold lever or two handles. Reliable, simple, easy to fit and replace.

Suitable for: most homes, especially renters or short-term ownership.

Pull-out spray (£150 to £400)

A spout that detaches into a flexible hose for filling pots away from the sink. Useful for big pans and cleaning.

Suitable for: serious cooks. The spray hose gets used often.

Boiling water tap (Quooker, Fohen, etc.) (£900 to £2,500)

An additional tap that delivers boiling water on demand. Replaces the kettle.

Pros: kettle replaced, instant boiled water for tea, pasta, blanching vegetables.

Cons: significant install cost (the tap is £900 to £1,800, fitting is £150 to £350, and you need a 13A socket and water filter underneath the sink). Filter cartridge needs replacing yearly (£40 to £80 each). The tank under the sink takes up cupboard space.

I install plenty of Quookers in London kitchens. Customers love them after the first month. Worth the cost if you make tea or coffee multiple times a day.

Filter tap (£200 to £600)

A small additional tap (often in chrome or brass) that gives filtered cold water. The filter sits under the sink.

Pros: better-tasting water for drinking. London tap water is safe but heavily chlorinated and tastes of it.

Cons: additional cabinet space for the filter unit. Filter cartridges every 6 months (£20 to £40).

Combined boiling and filtered tap

Some Quooker and similar units offer combined boiling, filtered, and ambient functions. Adds another £400 to £700 to the boiling tap cost.

Dishwasher position

Two practical considerations:

1. Plumbing connection. Needs a water supply (cold), a waste connection, and (usually) an electrical socket. The waste connects either to the sink waste below or to a separate spigot off the soil stack.

2. Cabinet sequence. Often goes immediately next to the sink for the shortest pipework run. Some kitchens want the dishwasher in a different position for ergonomic reasons (closer to the dining area, or on the cleaner side of the kitchen).

Moving the dishwasher more than 2 metres from the sink usually means adding a separate waste connection, which adds £150 to £300 to the plumbing cost.

If you have an integrated dishwasher (cabinet door on the front), the cabinet build cost is also higher. Worth specifying with your kitchen fitter.

Washing machine position

If your washing machine is in the kitchen (common in London flats and smaller houses), the considerations are similar to a dishwasher: cold supply (occasionally hot), waste connection, electrical socket.

Key issue in London: many older flats have shared waste connections that cannot handle the flow rate from a washing machine on a fast spin cycle. If the waste backs up into the sink during a spin cycle, you have undersized waste pipework. Standard fix is upgrading the waste pipe diameter from 32mm to 40mm and/or reducing horizontal pipe runs.

For Victorian terraces, washing machines now often go in a utility room or under-stairs cupboard rather than the kitchen, freeing up cabinet space.

Hot water flow at the kitchen sink

A kitchen tap that dribbles is annoying every day. The flow rate at any tap depends on:

• Mains pressure into the house
• Pipe size from the boiler to the kitchen (15mm or 22mm)
• Whether other taps are running at the same time
• The specific tap aerator

Quick check: turn on the kitchen hot tap and time how many seconds it takes to fill a 1-litre measuring jug. Under 6 seconds = good flow. 6 to 10 seconds = OK. Over 10 seconds = poor flow, worth investigating.

If your kitchen tap flow is poor, the renovation is the time to fix it. Options:

• Upsize the supply pipe from 15mm to 22mm to the kitchen
• Move to a more powerful combi boiler if the boiler is at fault
• Consider a system boiler with stored hot water for high-demand kitchens

Boiler position changes

Many London kitchen renovations involve moving the boiler. Common reasons:

• Existing boiler is in a kitchen wall cabinet that you want to use as a working cabinet
• Existing boiler does not fit the new kitchen layout
• Existing boiler is end-of-life and being replaced anyway

Moving a boiler is a significant job. Consider:

• New flue routing (must comply with regulations on positioning)
• New gas pipework
• New condensate routing
• New flow and return pipework to the heating system

Cost: £1,500 to £3,000 for a boiler relocation as part of a new install. More if extensive pipework changes are needed.

If you are renovating a kitchen and your boiler is over 8 years old, consider doing the boiler replacement at the same time. The kitchen is open, the floors may be up, the routing changes can be done in one go. Cheaper and cleaner than splitting the work into two projects.

Gas hob, electric hob, induction

A gas hob requires a gas pipe. If you are switching from electric to gas, the gas supply needs running to the hob position. Cost: £200 to £500 depending on routing.

Many London kitchens are switching the other way: from gas to induction. Reasons:

• Better control and faster heating
• Easier to clean (flat glass surface)
• No exposed flame (safer with kids)
• No combustion in the kitchen (better air quality)

If you are switching from gas to induction, the existing gas pipe to the hob position needs capping off properly (Gas Safe registered work). The kitchen circuit may need upgrading to a 32A supply for the induction hob. Worth combining with any other electrical work in the renovation.

Water filter or softener

If you live in central, east, or south London, your water is hard. Two options for the kitchen:

1. Inline filter for drinking water only. £100 to £200. Filters the cold supply to the kitchen sink (or to a separate filter tap).

2. Whole-house water softener. £900 to £1,800 fitted. Removes calcium from all water in the house, including drinking water (so you usually have a separate unfiltered drinking tap on the kitchen sink).

A renovation is the right time to install either. The work is easier with cabinets removed.

What I include in a kitchen plumbing quote

When I quote for the plumbing portion of a kitchen renovation:

• All first-fix and second-fix plumbing labour
• All sundries (fittings, sealant, valves)
• Removal and reroute of any existing pipework
• New isolation valves on every supply for future repairs
• Pressure testing of all new pipework
• Coordination with the kitchen fitter for sequencing

What is usually not included:

• The taps and sink themselves (you supply, plumber fits, or I source for an additional fee)
• The boiler if it is being replaced (separate quote)
• Tile work, kitchen unit assembly, electrical work (separate trades)

For a typical London kitchen renovation in 2026, the plumbing portion is usually £2,200 to £4,500 of the total project cost.

WhatsApp with a few photos of your existing kitchen layout and a rough idea of what you want changed, and I can quote the plumbing portion before the full job is designed. Often this helps you decide which layout changes are worth the cost.