Table of Contents
The short answer
The first thing to rule out, and very often the whole answer, is the simplest: the water that should be sitting in the trap under the grate has evaporated. Pour a jug of water into the drain, air the room for an hour and see whether the smell goes. In a guest bathroom, a maid's room or a home that has been closed over the summer, that is usually the entire repair.
If the smell stays, or returns within a day, there are four other causes worth knowing: a layer of slime and hair inside the drain, a trap that is missing a part or cracked so it cannot hold water, a venting fault that sucks the water out of the trap, and a partial blockage holding dirty water in the pipe. The first you can clean yourself. The other three need a plumber, and in a tower two of them may belong to the building.
IHR Dream Cleaning clears and checks floor drains in Abu Dhabi as part of its drainage and pipe unclogging service. This guide explains how to tell the causes apart, what is safe to do yourself and where to stop.
What a floor drain is supposed to do
Under the grate, the pipe dips into a bend or a small chamber that stays full of water. That water is the seal. Waste water flows through it, but air from the sewer side cannot pass back up. The seal is only a few centimetres deep, and nothing but the next flow of water tops it up.
In many bathrooms here the floor drain is more than an emergency outlet. The basin and the shower discharge into its trap under the floor, so the seal is refreshed every time someone washes their hands. A bathroom in daily use never has a dry trap. A bathroom nobody uses has no source of water for it at all.
Every smell from a floor drain comes down to one of two things. Either the seal has failed and sewer air is coming up the pipe, or the seal is intact and the smell is being made on your side of it, by what is growing in the drain.
Tell the smell apart first
The two kinds of smell are different, and so is their timing. A few minutes of observation saves a lot of guessing.
| What you notice | Likely cause | First check |
|---|---|---|
| Sewage or rotten-egg smell in a rarely used bathroom | Dried-out trap | Pour in a jug of water |
| Sour, musty smell strongest at the grate | Slime and hair in the drain | Lift the grate and look |
| Smell back within hours of adding water | Trap damaged or missing a part | Torch: is water standing in it? |
| Gurgling, and smell in bursts after a flush | Venting fault or partial blockage | Listen while another fixture drains |
| Slow drain with dirty water in it | Partial blockage | Does it take a jug of water quickly? |
| Smell low down by the toilet or at the basin | Not the floor drain | The cover test below |
The cover test: is it really the floor drain?
Before you treat the drain, prove it is the source. Dry the floor around the grate and tape a piece of cling film over it on all four sides, or lay a flat rubber sink stopper on top. Close the bathroom door and leave it for several hours, or overnight, with the extractor off. If the room smells fresh afterwards and there is a strong smell under the film when you lift it, the floor drain is the source. If the room still smells, look elsewhere: the basin overflow, the shower waste, the base of the toilet, or something that is not a drain at all.
Take the cover off afterwards. A floor drain is the room's protection against a flood and should not stay sealed.
Is the smell harmful?
Sewer air is a mixture of gases from decomposing waste. The rotten-egg note is hydrogen sulphide and the sharp note is ammonia. At the faint levels that reach a bathroom through a dry trap it is mainly unpleasant, but it is not something to live with. It can bring on headaches and nausea in some people, and an open trap is also an open door for cockroaches.
Two cautions are worth knowing. Hydrogen sulphide dulls the sense of smell, so a smell that seems to fade may not have gone. And sewer gas can contain methane, which burns, so never try to burn a smell off with a candle or a lighter held near the drain. If the smell is strong and someone feels unwell, leave the room, open the windows and get the drain looked at the same day.
Cause one: the trap has dried out
Water in a trap evaporates like water anywhere else, and conditions in an Abu Dhabi home speed it up. The air conditioning runs for most of the year and dries the indoor air. A home closed for summer travel may sit warm for weeks with the AC off or set high. A shallow seal in those conditions can be gone within weeks, and sooner in a hot utility room or on a balcony.
An extractor fan makes it worse in a way most people do not expect. A fan removes air from the room, and that air has to be replaced from somewhere. In a sealed apartment with the windows shut, the easiest way in may be the drain. While the seal is full, nothing comes through. Once it is dry, the fan actively draws sewer air into the room, which is why the smell can be strongest when the bathroom fan or the kitchen hood is running.
The places to suspect first are the guest bathroom, the maid's room bathroom, the laundry or utility room, the floor drain behind a washing machine, a kitchen floor drain, the balcony, and every drain in a home that has been closed.
- Pour about a litre of clean tap water slowly into the drain. Do the same for every other floor drain in the home, and run the tap for a few seconds in any basin, shower, bath or bidet that is not in regular use.
- Open the door, and a window if there is one, and let the room air for an hour.
- Close the door for a while and smell again. If the smell has gone, the dry seal was the cause.
- Set a reminder to top up unused drains every week or two. It takes a minute.
Before you travel
A trap filled on the day you leave will not last a long summer absence by itself. Fill every trap, then cover each floor drain with a flat rubber or silicone drain cover, or with cling film taped at the edges, to slow the evaporation, and put the plugs in the basins and the bath. Better still, ask whoever holds your keys to run each tap and pour a jug into each floor drain every couple of weeks.
When you return, remove the covers, top up the traps and air the home before you judge any smell. The rest of the reopening routine is in the guide to cleaning a home after summer travel.
Cause two: slime, hair and soap inside the drain
If the trap is full and the drain still smells, look at what is living in it. The underside of the grate, the walls of the drain above the water line and the trap itself collect hair, soap scum, skin oils and sand. Bacteria grow on that layer as a grey or black slime, and it gives off a sour, musty smell like a cloth left wet. Because it sits above the water seal, on your side of it, a perfectly good trap does nothing to stop it.
Warmth and humidity speed the growth, so the smell is usually worse in summer and in bathrooms without a working extractor. Small moth-like flies resting on the wall near the drain point to the same thing: drain flies breed in exactly this slime, as the guide to household pests in Abu Dhabi explains.
- Put on rubber gloves and lift the grate. Most sit loose in the frame or are held by one screw.
- Lift out the hair and debris by hand and bin it. If there is a removable cup or insert under the grate, note how it sits, lift it out and clean it too.
- Scrub the grate on both sides, the frame and the inside of the drain as far as a stiff brush reaches, using washing-up liquid or your ordinary bathroom cleaner. An old bottle brush is the right shape.
- Rinse with a jug or two of hot water from the tap. Do not use boiling water, which can soften plastic pipe.
- Refit the insert exactly as it was, replace the grate and top up the trap with clean water.
Bleach, descalers and perfumed blocks
Scrubbing does the work; chemicals only help afterwards. If you want to use household bleach, use it by itself, as its label directs, in a drain you have already cleaned and rinsed. Never follow or precede it with a descaler, a toilet cleaner or any acidic product. Bleach and acid release chlorine gas, and a bathroom is the one room where both are kept side by side.
Do not pour a caustic or acid drain opener into a floor drain to cure a smell. It does nothing for a dry or missing seal, it sits in a trap that your basin and shower may also drain through, and it can damage stone floors and metal grates. Perfumed blocks and scented disinfectants mask a smell for a day and change nothing.
The same slime elsewhere in the bathroom
The overflow slot of a basin leads to a hidden channel that is never rinsed, and it can smell exactly like a drain. Clean it with a thin bottle brush and soapy water. A linear shower channel has a long cover and often a hair basket beneath it; lift both and scrub the channel. The pop-up plug of a basin carries a plug of hair on its stem. All three are common sources of a smell that gets blamed on the floor drain.
Cause three: a trap that is missing, damaged or badly fitted
A trap can only hold a seal if all of it is there. Some floor drains keep their seal in a removable insert under the grate, a small cup or bell that is lifted out for cleaning. If it was not put back, was refitted upside down, has cracked or has been lost, the drain is an open pipe however much water you pour into it. Other drains have the trap built into the pipe under the floor. That kind can crack, can lose its water through a leaking joint, or can turn out to have been installed without a proper trap at all, which sometimes comes to light after a renovation or in a newly built bathroom.
The torch test tells you which situation you are in. Lift the grate, pour in a jug of water, wait a minute and shine a torch down. You should see still water a short way below the grate. If you see a dry pipe, or the water level drops as you watch, the trap is not holding.
A missing insert is sometimes a matter of finding it in the cleaning cupboard and refitting it. Anything else here is a plumber's job. Do not chisel out the grout around the drain body, do not try to seal a cracked trap from above with silicone, and do not pack the drain with anything. A plumber can fit the correct part, and where a drain cannot hold a water seal reliably there are one-way inserts that sit under the grate and close when no water is flowing. Whether one suits your drain depends on its size and type, so that is decided on site. This is repair work, and it comes under our plumbing repair service.
Cause four: a venting fault that empties the trap
Water falling down a pipe pushes air ahead of it and pulls air in behind it. Drainage systems have vent pipes so that this air can move freely. When a vent is blocked or missing, or a partial blockage narrows the pipe, the moving water has to find its air somewhere else, and the nearest source is the trap of a nearby fixture.
It shows in two ways. Suction behind the flow pulls the water out of the trap, and you hear a gurgle from the floor drain just after a toilet is flushed or a bath is emptied. Or pressure ahead of the flow pushes bubbles up through the seal, and you get a burst of smell and a glugging sound when water runs elsewhere in the building. Either way the pattern is distinctive: the smell comes in bursts linked to water use, the seal you refilled is low again the same day, and often more than one bathroom is affected.
You cannot fix venting yourself and should not try. In a tower the stack and its vents are common parts of the building, so report it to building management and describe exactly what you hear and when. Where work touches shared plumbing, the building may need to approve it or isolate the supply first. In a villa the vent pipes end above the roof, where they can be blocked by debris or a bird's nest. That is a job for a plumber with safe roof access, not for a resident on a ladder.
Cause five: a partial blockage
A drain that takes a long time to swallow a jug of water is holding dirty water and debris in the pipe, and that decomposes and smells whatever the state of the seal. It often comes with the gurgling described above, because a narrowed pipe disturbs the air flow in the same way a blocked vent does. If the basin and the shower in the same bathroom are also slow, the restriction is probably in the floor drain's trap, which they share.
Clear what you can reach by hand, as in the cleaning steps earlier. Beyond that the drain needs mechanical clearing by a technician. The safe things to try first, and the signs that a blockage is in the building's shared line and not in your flat, are in the guide to blocked drains and whether drain cleaners work.
Smells that are not the floor drain
If the cover test cleared the floor drain, these are the other usual sources in a bathroom.
- The base of the toilet. The joint between the pan and the floor pipe is sealed, and if that seal fails, sewer air escapes at floor level. Signs are a toilet that rocks, staining around the base and a smell that is strongest low down beside the pan. A plumber needs to reseat it.
- Black silicone and damp grout. Mould in the sealant around a shower tray or bath gives a musty smell, not a sewage one. Once the black has grown into the silicone it does not scrub out and the joint needs renewing, which is the work of our grout and silicone repair service. How to judge it is in clean it or redo it.
- Water under the floor or behind the wall. A slow leak keeps tile adhesive and screed wet, and stale water smells earthy. Look for tiles that sound hollow, grout that never dries and damp at the foot of the wall in the next room, and read the signs of a hidden water leak.
- The air conditioning. A musty smell that arrives when the AC starts and is strongest at the vent belongs to the unit or the duct, as described in musty smell or black spots on AC vents.
- The extractor duct. In a tower the bathroom fan usually discharges into a shared shaft. Cooking or smoke smells that arrive through the fan grille when the fan is off are coming back along that route, and that is one for building management.
- The washing machine. A machine that smells sour inside, or a waste hose pushed loosely into an open pipe, is often mistaken for the floor drain beside it.
Where to stop
Everything a resident can safely do to a floor drain is done from above, by hand, with water, a brush and ordinary cleaner. Beyond the cautions already given, the limits are these.
- Do not seal a floor drain permanently with silicone, tape or a tile. A temporary cover while you travel is fine; a permanent one leaves the room with no outlet if a hose bursts.
- Do not remove anything that is fixed, cemented or below floor level.
- Do not push rods, wire or a hose down the pipe. They pack debris tighter and can damage the trap.
- Do not ignore dirty water rising in the drain. Stop using water in that bathroom and tell building management or call a plumber.
When to call, and what to expect from the visit
Call when the smell returns within a day of refilling the trap, when the torch shows no standing water, when you hear gurgling, when the drain is slow or holds dirty water, when more than one bathroom smells, or when the smell is at the base of the toilet. In an apartment, tell building management at the same time if more than one drain or more than one flat seems to be involved.
What to tell us when you book
A smell cannot be photographed, so the description matters more than usual.
- Which drain it is, and whether the bathroom is used daily or rarely.
- What kind of smell, and when it is worst: all the time, in bursts, when the fan runs, after a flush.
- What happened when you added water, and how long the improvement lasted.
- Whether the drain is slow, and whether any other drain gurgles or smells.
- Any recent renovation, tiling or drain cleaning.
- Apartment or villa, which floor, and whether the home is rented.
- A photo of the drain with the grate lifted.
How it is priced
Drain clearing has no published price list, and a plumber's visit starts from AED 99 for the first hour on site. Either way the job is quoted from your description and photos, or after a free inspection where the drain has to be seen, and the figure is agreed before work starts. Any part is shown and priced to you before it is fitted. Payment is online by card from My bookings on this website once the price is confirmed, and every quote includes VAT.
On the day
The work needs access to the drain, to the other floor traps nearby and, in a villa, sometimes to the outside chamber. At the end the technician runs water through every drain that was cleared, with you, and checks that nothing backs up in the floor traps. Ask to be shown the standing water in the trap with a torch before the grate goes back. It is the one thing that proves the seal is there.
A routine that keeps the smell away
None of this takes long, and most of it can be added to the normal cleaning of the bathroom. If someone cleans your home regularly, ask for the unused drains to be topped up at each visit. Limescale, grout and mould in the rest of the room are covered in the guide to bathroom deep cleaning.
| When | What to do | Why |
|---|---|---|
| Every week or two | Pour water into unused floor drains; run unused taps | Keeps every seal full |
| Every month | Lift the grate, remove hair, scrub grate and drain | Stops slime building up |
| After each shower | Run the extractor and leave the door open | Dries the room |
| Before travel | Fill traps, cover floor drains, plug basins | Slows evaporation |
| On return | Remove covers, top up traps, air the home | Restores the seals |
Common questions
I pour water in and the smell is back by evening. Why?
A full trap does not empty itself in a day by evaporation. Either the trap is not holding water, or the water is being pulled out by suction when another fixture drains. Do the torch test, and listen for gurgling when the toilet is flushed. Both causes need a plumber, and the second may be the building's to fix.
Can I pour bleach down the drain every week?
You can, as the label directs, but it is not doing what you hope. It refills a seal no better than water does, and it flows past most of the slime, which is above the water line and under the grate. Scrubbing removes the slime; bleach only disinfects what it touches, for a short time. Never use it in the same session as a descaler or any acid cleaner.
The bathroom is new, or newly renovated, and it smells. Why?
A bathroom that has never been used may simply have a trap nobody has filled. If water does not cure it, the usual suspects after building work are debris in the trap, such as tile adhesive, grout or sand washed down during the work, an insert that was removed and not refitted, or a drain connected without a proper trap. Report it to the contractor, the landlord or the developer while the work is still recent.
Do drain covers and anti-odour inserts work?
As a second line of defence, yes. A cover slows evaporation in a drain that is rarely used, and a one-way insert closes the pipe when no water is flowing. Both collect hair and need cleaning, and neither fixes a blocked pipe, a cracked trap or a venting fault. Fit one after the cause has been found, not instead of finding it.
Is this the landlord's job or mine?
It depends on your tenancy contract and on where the fault is. Topping up traps and cleaning a grate is ordinary housekeeping. A cracked trap, a venting fault or a blocked stack is a defect in the property or the building. Read the maintenance clause, tell the landlord or the agent in writing, and in a tower tell building management as well. We cannot state who pays as a rule, because it is not one.
How soon can someone come?
Urgent drain problems are often scheduled for the same day when the diary allows, at no extra charge, and we work every day from 8 AM – 8 PM. Dirty water rising in a drain is urgent. A smell that a jug of water cures is not, and can wait for a time that suits you.
How to book
Book on the website or in the IHR Dream app and describe the smell using the list above, then reply to the confirmation email with a photo of the drain. We confirm the scope and the price before the visit. The drainage and pipe unclogging page sets out what the service includes. When you are ready, book a visit.
