Is a Blocked Drain an Emergency? How to Tell in Two Minutes

A blocked drain is an emergency when foul water is coming back up inside the property, or when every toilet, sink and shower in the house is backing up at the same time. A single slow sink, a gully outside holding water after rain, or a blocked second toilet is a nuisance, not an emergency, and can usually wait until the morning. The rest of this page is the quick check we run through on the phone, so you can run it yourself before deciding whether to pay for a night call-out.

The short answer: it depends where the water is going

What makes a blockage urgent is not the blockage itself but where the waste water ends up. If it is backing up into rooms people live in, it is an emergency; if it is sitting in a pipe or an outside chamber, it usually is not.

Every drain in a house runs downhill to one main pipe, and that pipe runs to the sewer. When the main pipe blocks, the water from every fixture upstream has nowhere to go, so it rises to the lowest open point it can find. In most London houses that is a ground-floor toilet, a shower tray or an outside gully. In a basement flat it is often the flat itself. That is why the same blockage can be an annoyance in one property and a flood in the next.

Four signs that make it an emergency tonight

Call out of hours if any of these are happening now. Each one means waste water is already inside, or will be within the next few flushes.

• Sewage rising through a toilet, shower or floor drain. If the water in a ground-floor WC climbs when someone upstairs flushes or runs a bath, the main drain is blocked below it.
• Every outlet in the house is slow or backing up at once. One slow basin is a local blockage. All of them together means the shared pipe is blocked, and it will get worse with use.
• A manhole or gully has overflowed and is running towards a door, air brick or lightwell. Once foul water reaches the building fabric the clean-up cost quickly outweighs the call-out.
• You are in a basement or lower-ground flat. Gravity works against you. A blockage that shows as a slow drain upstairs arrives as sewage in your bathroom.

If you are seeing any of these, the emergency drainage service is the right route, and it is worth calling before the next person in the house uses water.

Blockages that can safely wait until morning

If nothing is coming back up inside and you still have a working toilet, waiting until 7am is usually the sensible choice. You get the same clearance at the standard rate instead of the night rate.

Typical examples: a kitchen sink that is slow but emptying, a single blocked basin or bath, a second bathroom out of action when another one works, and an outside gully full of leaves after a downpour with nothing backing up indoors. None of these gets dramatically worse overnight if you stop using the affected outlet. We will say so on the phone if that is where you are, because a night rate for a job that could have waited is a bad deal for you.

The two-minute check: which drain, and how far down

Two questions tell you most of what an engineer needs to know: is it one outlet or several, and is the nearest outside manhole full or empty? You can answer both in a couple of minutes without tools.

First, run the cold tap in each basin for ten seconds and flush one toilet. If only one fixture misbehaves, the blockage is in that fixture's own pipe, close to the house, and it is rarely urgent. If several misbehave, the problem is further down.

Second, find the inspection chamber, usually a square or rectangular cover in the front path, side return or back garden. If you can lift it safely, look inside. A chamber full of standing water means the blockage is downstream of it, towards the sewer. An empty chamber while your fixtures are backing up means the blockage is between the house and that chamber. Do not climb in, and do not leave the cover off with children or pets about. Our guide to the early signs of a blocked drain covers the slower warning symptoms in more detail.

What to do while you wait, and what not to do

Stop using water. That one step does more to limit damage than anything else you can do before the engineer arrives.

• Tell everyone in the house not to flush, shower, run the washing machine or use the dishwasher.
• Move rugs, bags and anything valuable away from low-level toilets, shower trays and floor drains.
• If waste water has come in, keep children and pets out of the room and wash hands after touching anything it reached.
• Do not pour chemical drain cleaner into a drain that is backing up. It will not shift a main-drain blockage, and it sits in the water the engineer then has to work in.
• Do not keep plunging a ground-floor toilet when the main drain is blocked. You are pushing water against a full pipe, and it has to come out somewhere.

Who should pay: you, the landlord or the water company

If the blockage is in a pipe that only serves your property and sits inside your boundary, it is usually yours. If the pipe is shared with neighbours or runs beyond the boundary, it is often the water company's, and they clear it without charging you.

Since October 2011, most shared drains and lateral drains outside the property boundary in England have been the responsibility of the sewerage company. If your chamber is empty but the next one down the road is full, or several neighbours are affected at once, call the water company before paying anyone. Tenants should tell their landlord or managing agent first unless sewage is actively coming in and nobody can be reached. The article on who is responsible for a shared drain blockage walks through the boundary rules.

How the time of the call changes the price

We charge by time band set by the clock: 7am to 5pm, 5pm to midnight, and midnight to 7am. The same clearance costs more at 2am than at 2pm, and the figure for each band is agreed on the phone before anyone travels.

That is the practical reason the emergency question matters. If the check above says it can wait, waiting saves money for the same work. If it says it cannot, the difference between two bands is small next to replacing a floor. Current figures for each band are on the pricing page.