Sewage Coming Up Through the Drain or Toilet: What to Do Right Now

If sewage is coming up through your shower, bath, floor drain or toilet, stop using every tap, toilet and appliance in the property now. Dirty water rises through the lowest opening in the house when the pipe below it cannot discharge, and every flush or wash upstairs adds to what comes out downstairs. Once the water stops rising, you have time to work out whose problem it is and how urgently it needs a van.

Why sewage comes up through the lowest drain in the house

Sewage appears at the lowest fitting because that is where the pressure of a backed-up pipe finds its way out first. A ground-floor shower tray, a basement WC or an external gully sits below everything else connected to the same run, so it floods first.

There are only two broad causes. Either the private drain between your house and the sewer is blocked, so your own waste has nowhere to go, or the public sewer in the road is full, so water is pushing back up your connection. The first is common and usually cleared in one visit. The second is less common, tends to happen during or after heavy rain, and is the water company's responsibility rather than yours.

The first ten minutes: what to do before anyone arrives

Stop all water use, keep people and pets away from the affected room, and do not try to push the blockage through with a plunger while sewage is standing in the tray or bowl. That is the whole of the urgent list.

• Tell everyone in the building. In a house of flats, upstairs neighbours flushing is often what keeps the level rising. A note on the stairs or a knock on the door does more than anything else you can do.
• Turn off the washing machine and dishwasher. A pump-out cycle discharges a large volume very quickly, and it will come straight back up through the lowest opening.
• Keep the room shut and ventilated. Open a window if it is safe to, close the internal door, and keep children and pets out. Sewage carries bacteria that you do not want walked through the house.
• Lift what you can off the floor. Rugs, bags, boxes and electrical items near the affected room. If water is approaching sockets or an extension lead, switch that circuit off at the consumer unit if you can reach it without standing in water.
• Take photos before you clean anything. If you later make an insurance claim, pictures of the water level, the affected rooms and the date and time are worth far more than a description.

Avoid chemical drain cleaners. They will not shift a blockage in a 100mm drain, and they make the water more dangerous for whoever has to open the chamber afterwards.

Is it your drain or the public sewer?

If only your property is affected and the weather is dry, it is almost always a blockage in your private drain. If neighbours are also affected, or it started during heavy rain, the public sewer is the more likely cause.

Two quick checks help. First, lift the cover of your own inspection chamber if you have one and it is safe to do so. If the chamber is full to the top, the blockage is further downstream, either in a shared section or in the sewer itself. If the chamber is empty or flowing, the blockage is between the chamber and the house, which makes it a private drain problem and usually a quick clearance. Second, ask the neighbours on either side. Several houses backing up at once points towards a shared run or the public sewer.

Since October 2011, pipes that serve more than one property and those that run outside your boundary have generally been the responsibility of the local water company, which in most of London is Thames Water. Drains serving only your property and within your boundary remain yours. Our guide to who is responsible for a shared drain blockage walks through the boundary in more detail.

When sewage backing up is a same-night emergency

Any sewage discharging inside a home is worth a same-night call-out. The exceptions are narrow: the level has stopped rising, the affected fitting is not in a living space, and you have another working toilet.

The situations where waiting until morning is a bad idea:

• Foul water in a basement flat or a ground-floor room with flooring, skirting or furniture at risk.
• The only WC in the property is the one backing up.
• The level is still rising even with all water use stopped, which means someone else upstream is still discharging into the same run.
• Sewage is reaching a doorway, a lightwell or a neighbour's property.

Where it has stopped, it is outside or in a utility room, and you have another toilet, the same job at 7am is billed at the standard band rather than the night band. We will tell you that on the phone rather than send a van you did not need. The three time bands and what the night rate pays for are explained separately.

What the engineer does when they arrive

The engineer's first job is to find the nearest access point downstream of the blockage and relieve the pressure, so the standing sewage drains away before anything else happens. After that the work is a normal clearance.

In practice that means lifting the chamber covers to find which one is full and which one is empty, then working from the empty side back towards the blockage with rods or a jetting hose. Once the run is flowing, a camera goes down to check it is properly clear rather than just punched through, and to see whether the cause was something flushed, a build-up of fat and scale, or a structural fault such as a displaced joint or root ingress. You can read how blocked drain clearance is carried out on its own page.

If the camera shows the blockage is in the public sewer rather than your drain, the engineer will say so, stop, and you can report it to the water company. Clearing a public sewer is their job, not something you should be paying a private contractor to do.

Cleaning up and stopping it happening again

Once the drain is flowing, treat everything the sewage touched as contaminated. Hard surfaces can be cleaned with hot water and a household disinfectant while wearing gloves. Carpets, underlay and soft furnishings that have been soaked in foul water are normally not worth saving.

Whether it happens again depends on the cause. A one-off blockage from wipes or sanitary items will not come back if they stop going down the toilet. A blockage caused by fat, scale or a sagging pipe will, and that is the point where a camera survey and a planned repair cost less than repeated emergency call-outs. If the property floods from the public sewer during heavy rain more than once, ask the water company about a non-return valve on your connection. It is a common fix for basements in low-lying streets.

If you are going to claim on home insurance, keep the engineer's report and any camera footage. Most policies ask what caused the escape of water, and a written finding from the visit answers that far better than a description after the fact.