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Most of it happens behind tile, which is what sets shower plumbing apart from other fixtures. A valve set at the wrong depth, a drain that doesn't line up with the pan, or a connection that weeps inside the wall can go unnoticed until the grout or the ceiling below shows the damage. Good work is planned together with the waterproofing and finishes, not after them.
The shower is also where many scald injuries happen, so the valve's temperature control deserves as much attention as its look.
Pressure-balancing vs thermostatic shower valves: how each controls temperature
Most shower valves are one of two kinds. A pressure-balancing valve reacts to changes in water pressure: when someone flushes a toilet and the cold-water pressure drops, it cuts back the hot side to match, so the shower doesn't suddenly turn scalding. A thermostatic valve senses temperature instead and holds the mix you set, and it usually separates temperature from volume, so you can turn the flow down without changing how hot it is.
- Pressure-balancing: the common single-handle valve, compact and easy to service; it handles pressure swings well, though the mix can drift as the incoming cold water gets colder in winter.
- Thermostatic: steadier temperature and separate volume control, well suited to showers with several outlets such as a rain head, a handheld and body sprays; the valve and trim are larger and more involved to install.
- Limit stop: both types have an adjustable stop that caps how far the handle turns toward hot; it should be set at installation and rechecked whenever the water heater setting changes.
- Diverters: a shower with more than one outlet needs a diverter or transfer valve to route water between them, and it has to be planned at rough-in.
Shower scald prevention: anti-scald valves and water heater temperature
Hot water has to be hot at the heater and safe at the showerhead, and those are two different settings. The Government of Canada recommends keeping the water heater at 60°C (140°F) to prevent the growth of bacteria such as Legionella, and installing automatic mixing valves on showers, tubs and faucets, or an anti-scald mixing valve at the water heater, set to deliver hot water at 49°C (120°F). It also warns that a child's skin burns in a quarter of the time it takes an adult's.
Plumbing codes set requirements for temperature control in new showers, and a licensed plumber will install a valve that meets the local code and set its limit stop. If an older shower still has two separate handles, or jumps from hot to cold whenever another fixture runs, that's a good reason to replace the valve, especially in a home with young children or older adults.
Moving or adding a shower: drain location, venting and floor slope
A shower can go almost anywhere a drain can reach. It needs a trap directly below the drain, waste pipe sloped toward the stack, and a vent that keeps the trap's water seal from being siphoned away. In a wood-framed house that means running pipe through or between joists; in a basement it often means cutting the slab to reach the drain line beneath it. Because this changes the drain and vent system, it calls for a licensed plumber and, in many municipalities, a permit.
The shower floor matters just as much. Whether it's a prefabricated base or a mortar bed under tile, the pan has to slope evenly to the drain so water doesn't pond in the corners.
- Check which way the joists run before fixing the drain location, since that decides whether the pipe can reach the stack without cutting framing.
- Choose the valve, trim and showerhead before rough-in: each valve body accepts only its own trim, and it has to sit at the depth the finished wall requires.
- Plan an access panel behind the valve where the layout allows, so a cartridge or a leak can be reached without removing tile.
Curbless showers and linear drains: what the plumbing has to allow for
For the plumber, a linear drain changes where the trap goes. The channel runs along a wall or across the entrance, and its outlet has to line up with a trap and waste line below, often in a joist bay that must be free of framing. A curbless entry also puts the drain lower than in a standard shower, so the floor can slope to it without a step. Ask whether the drain chosen can keep up with every outlet running at once, particularly with a rain head.
Recessing the subfloor, reinforcing joists and carrying the waterproofing beyond the shower area are part of a bathroom renovation, where the plumber, the framer and the tile setter plan the work together.
Shower waterproofing and the plumbing: drain flanges, valve openings and pipe penetrations
The membrane behind the tile is usually installed by the tile setter or renovation contractor, but it only works if the plumbing suits it. The drain has to match the membrane system, with a flange or clamping ring the membrane can bond or seal to; the valve and shower arm need openings that can be sealed with the gaskets or collars made for them; and nothing should pierce the membrane that wasn't planned.
Before the walls close, ask the plumber to pressure-test the new supply piping and confirm the drain connection is sound. A leak caught at that stage means an afternoon of work, not a tiled wall coming down.
Signs of a shower leak behind the wall or under the floor
A shower leak can come from the supply piping, the valve body, the drain connection or failed waterproofing, and each is repaired differently. A plumber or leak detection specialist can narrow it down before any tile comes off.
- A stain or bubbling paint on the ceiling below the shower, or on the far side of the wall behind it.
- Grout or caulk that stays dark long after a shower, or tiles that sound hollow or feel loose.
- Water on the floor outside the shower that isn't from splashing, or a baseboard that swells.
- A musty smell that doesn't clear with the exhaust fan running.
- A showerhead or spout that keeps dripping after the valve is closed, which points to the cartridge.
Low-flow showerheads: water efficiency and Canada's showerhead flow limit
The showerhead is the easiest part of shower plumbing to change, and one of the most effective for water use. The Capital Regional District in British Columbia notes that high-efficiency showerheads use between 5.6 and 7.6 litres per minute, compared with up to 20 litres per minute for older models. Federal energy efficiency regulations now cap showerheads manufactured on or after July 1, 2026 at 7.0 litres per minute, measured at a standard test pressure. Less hot water used also means less work for the water heater.
If a new efficient head feels weak, clean its nozzles and check that the shower valve and shut-offs are fully open before blaming the head; in hard-water areas, mineral scale clogs the nozzles over time.
Shower Plumbing: frequently asked questions
Why does my shower go hot or cold when someone flushes the toilet?
The flush draws cold water away from the shower. A pressure-balancing or thermostatic valve compensates for that; an older valve without either can't. If yours has one and still swings, the cartridge may be worn or clogged with scale and can usually be replaced.
Can a shower valve be replaced without removing the tile?
Sometimes. If there's an access panel behind the shower, or the wall behind it is drywall in a closet or bedroom, the plumber can work from that side. From the tiled side, the opening is limited to what the new trim plate will cover, so a valve whose trim hides the old opening is often the deciding factor.
What temperature should my shower water be?
The Government of Canada recommends mixing valves set to deliver hot water at 49°C (120°F), with the water heater itself kept at 60°C (140°F) to control bacteria. A plumber can set the limit stop on your shower valve and check the temperature at the head.
Do I need a permit to move a shower?
Often, yes. Moving a shower means a new drain, trap and vent connection, and many municipalities require a permit and an inspection before the walls and floor are closed. In Quebec, the work falls under the RBQ plumbing licence; elsewhere, check with your municipality and the provincial licensing body.
Is a low-flow showerhead a good idea if my water pressure is already low?
It can still work well, but deal with the pressure problem first. Clean the existing head, make sure the valves are fully open, and have a plumber look at the supply if the whole house is weak. Then try an efficient head before assuming it will feel worse.
Sources
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides