My neighbour’s teenage lad hammered on my door at half-seven on a Sunday, hair still lathered and panic in his eyes. “Auntie Linda, the shower’s grown a paddling pool and Mum’s on her way back from shift!” I followed the trail of sudsy footprints to their upstairs bathroom; the tray was brimming like a birdbath, each fresh droplet from the mixer raising the level another fraction. His sister’s plastic dinosaur was doing its best impression of the Loch Ness monster. I stuck a gloved finger through the grate, fished out a Medusa of black hair wrapped round a Lego brick, and the whole lot glugged away in three greedy gulps. He stared like I’d performed actual witchcraft. That tiny plug of mess had cost them a morning of stress and, if left longer, could have cost the ceiling below. Standing water in a shower isn’t just a nuisance—it’s the house’s way of waving a red flag before real damage starts.
This guide focuses on slope installation prevents pooling. For comprehensive installation procedures, see our complete shower drain installation guide.
Who I Am and Why You Can Trust This Advice
I’ve been a licensed plumber and Part P-registered drainage engineer for twelve years, with over 1,400 shower trays lifted, 800 waste pumps replaced and more hairballs named than I care to admit. I hold a Level 3 NVQ in Domestic Plumbing, am on the WaterSafe register and carry NICEIC approval for any electrics that wet-room pumps involve. Last spring I was called to a boutique hotel where three en-suites had backed up simultaneously; a single displaced gasket in the shared soil stack had turned their glossy brochure photos into wading-pool horror stories. We stripped, descaled and resealed everything inside a working day, saving the manager a full week of lost bookings. I’ve seen the good, the bad and the frankly furry—so when I talk about standing water, I’m talking from soggy boots-on-the-ground experience.
Quick Steps:
1. Remove the grate or hair catcher—most pop out with flat screwdriver pressure at the edge.
2. Look for visible blockage; if water is slower than a coffee percolator, there’s debris within arm’s reach.
3. Plunge using a dedicated shower plunger (cup rim fits 2″ waste); block overflow with wet cloth so force focuses on trap.
4. Flush with 2 litres of just-off-boiling water mixed with two tablespoons of washing-soda crystals—cheaper than Mr Muscle Drain-Unblocker (£2.50 supermarket vs £6.49 aerosol) and kinder to seals.
5. Replace grate; run shower 30 seconds. If depth still exceeds 5 mm after one minute, move to mechanical removal (see section on traps).
What “Standing Water” Really Means
Any puddle deeper than a fifty-pence piece (≈ 2 mm) that’s still there five minutes after the flow stops counts as standing water. A properly laid tray should empty almost completely; the residual film dries off rather than pooling. Persistent depth points to partial blockage, gradient error, or a membrane that’s bowed and is now acting like a mini-dam.
I once saw a luxury stone resin tray in a £750k loft conversion holding a lake the size of a dinner plate. The installer had set the waste body level instead of sloping the former; water simply couldn’t climb uphill to escape. We had to break out four tiles, re-pack the subfloor with quick-set mortar and reset the tray at 1:40 fall—two days’ grief for a five-minute check with a spirit level first time round.
Common Causes (and the Smell That Follows)
Hair is public enemy number one, but add soap scum and you get concrete. Combine that with the plastic ridges inside McAlpine HT102 traps (good design, but great at snagging fibres) and flow rate halves in months.
Second culprit: hard-water scale. In Reading we run 280 ppm calcium; that’s enough to choke the 5 mm slots of a standard Mira flight-level strainer in under a year. The giveaway is a white rim around the grate and a sulphur odour—anaerobic bacteria throwing a party in the stagnant layer.
Third, and priciest, is pipe deformation. If someone’s driven a screw through the 40 mm solvent weld trying to fix a bath panel, the pipe narrows and acts like a dam. I diagnosed that exact scenario in a 1930s terrace; water backed up only when the washing machine dumped its load into the same soil stack. Camera survey (£95 at PTS Hire, Watford) revealed the screw tip glittering like a tiny sword.
Tools That Actually Work
- Silverline 633135 4″ suction plunger – £8.99, Screwfix. Flared rim seals better than the classic red cup.
- Rothenberger Ropump 7-litre pressure pump – £38.40, Toolstation. Gives a controlled blast without cracking old clay sockets.
- Drainage hair snake, 3 m barbed plastic strip – £2.29, Home Bargains. Safer on chrome wastes than metal augers.
- Wera Kraftform mini-screwdriver set – £11.50, Amazon. Removes most pop-up plugs without chewing the chrome.
Keep a separate set for bathrooms; you don’t want toilet bacteria hitching a ride to the shower tray you’re cleaning.
Step-by-Step: Clearing a Hair-Clogged Trap
1. Pop the grate. If it’s silicone-sealed, slice gently with a Stanley knife; reseal afterwards with GeoCel 201 (£4.80, 80 ml tube).
2. Shine a torch. See a dark mat? That’s the hair quilt. Wear Marigold and lift; it comes out like a jellyfish.
3. Insert barbed strip, twist, pull. Expect resistance—feel for the ‘give’ when you pass the water seal (usually 50 mm down).
4. Pour washing-soda mix, wait 10 min. It saponifies body oils, making next pull easier.
5. Reassemble, run shower full bore 60 seconds. Depth should stay under 2 mm. If not, move to pipework.
I cleared a student house in Clapham using those exact moves; they’d postponed calling me for three months because the letting agent quoted £180 plus VAT. Total cost of DIY: £2.29 strip + 30 p of soda. They spent the savings on pizza, and I gained four grateful tenants who now recommend me on their uni group chat.
When the Waste Itself Is the Problem
Standard 90 mm shower wastes flow 24 l/min at 15 mm head—fine until you fit a rainfall drencher kicking out 28 l/min. Result: water arrives faster than it leaves, so you stand in your own puddle.
Upgrade options:
- Hi-Flow 50 mm trap (Wirquin Neo, £26, Travis Perkins) rated 34 l/min. Needs 65 mm hole in tray—check before you buy.
- Wedi Fundo 75 mm linear waste (£89, Wickes) shifts 42 l/min and hides under a slit at the edge—great for level-access builds.
Time budget: swapping like-for-like takes 45 min; enlarging the hole adds another hour with a 68 mm diamond core. Charge-out in London? £150 labour plus parts. Do it during a retile and you save the call-out fee.
Hidden Structural Issues
Fall too shallow? UK Building Regulations Part H call for 1:40 minimum on shower room floors, but that’s for surface water; the tray itself should self-drain to waste. I check with a 600 mm spirit level and pack of 10 mm coins. If the bubble centres when one coin is under the low end, you have roughly 1:60—too lazy.
Membrane ballooning? If the tanking layer (your waterproof jacket) isn’t glued to the former, water creeps underneath and lifts like a blister. Smells musty, and the tray flexes slightly when you step in. Remedy: strip tiles, refit Wedi Subliner Dry with fresh sealing tape, retile. Materials £110, labour one day. Ignoring it risks joist rot—then you’re into £2k carpentry territory.
Safety Considerations and Legal Requirements
Working on waste pipes is generally DIY-friendly, but two areas cross legal lines:
1. Soil-stack modifications inside a dwelling must be notified to Building Control if you change diameter or vent arrangement (Part H, 1.7).
2. Any electrical shower pump (common in basement conversions) comes under Part P; connection must be by registered electrician or signed off via local authority.
Always isolate the shower pump at the fused spur before prodding around with metal tools. Water and 230 V don’t mix—trust me, 30 mA across wet skin ruins your week.
Warning: Pouring straight boiling water onto acrylic trays causes crazing—tiny cracks that void warranty and weaken the tray. Keep kettle water below 80 °C or add cold first.
Cost & Time Reality Check (2025 Prices)
- Plunger + soda DIY fix: £3–£10, 15 min.
- Professional de-clog (within 15 mi): £75–£95 first hour, includes mini-cam check.
- Trap upgrade to hi-flow: £45 parts + £90 labour, 1–2 h.
- Full tray reset for gradient: £350–£500, one day, includes skip for rubble.
A client in Solihull balked at the £95 call-out, tried four bottles of One Shot 80% caustic (£7.99 each) over a weekend. The stuff ate the rubber seal, waste began to weep into the joists, and the bill to open the kitchen ceiling below came to £480. Cheaper isn’t always cheaper.
How can I stop hair reaching the trap?
Fit an aftermarket stainless hair catcher such as the TubShroom Ultra (£14.99, Amazon). Empties in seconds, catches 95% of shed before it knots inside the grate. Rinse under hot tap weekly.
Is a bit of standing water actually harmful?
Yes. Above 2 mm depth takes longer than 30 min to evaporate, letting bacteria breed. That leads to biofilm—black slime that smells of rotten eggs and reduces pipe diameter permanently.
Can I use a wet vacuum?
Only if the manufacturer states “wet pick-up” and you remove the paper filter first. I use a Karcher WD3 V-17/4 (£89, Screwfix) with the rubber gulper nozzle; it yanks up hair in one slurp. Empty immediately—never let greywater sit in the drum.
Does shaving foam block drains faster?
Believe it or not, yes. The stearic acid reacts with calcium and forms waxy clumps that glue hair together. Rinse the tray for ten extra seconds after a shave and you’ll halve blockage frequency.
What if the water only rises when the kitchen sink is emptied?
Shared horizontal branch. Water from the sink is pushing air and backflow up the shower waste. Likely cause: partial blockage downstream, often grease. Needs rotary mechanical cleaning (R600 machine hire £45 day rate) or call a pro.
Conclusion
Standing water is your shower’s quiet SOS. Ignore it and you graduate from a five-minute plunger job to replacing joists and ceilings. Tackle it early—pop the grate, pull the hair, respect the gradient—and you’ll keep those feet dry for the price of a coffee. If the puddle outruns your DIY, phone someone qualified before the smell phones you. Your floorboards, your wallet and whoever cleans the bathroom next will thank you.