When a named storm is forecast for London, the Met Office usually gives a little warning. In that window, a few simple drain checks can cut your flood risk. Not every London home is at risk. Yet homes in low-lying areas, homes with a history of drain trouble, and homes on old combined sewers face real risk in intense rain. Here are five checks that take little time and can make a big difference.
Check 1: Clear Every External Gully and Downpipe Outlet
This is the highest-impact check, and it is quick. Gullies in the rear garden, front path and side passage collect debris all the time. So do downpipe outlets. Leaves, moss, silt and small stones slowly cut the inflow. You do not notice this in normal rain. In a storm, however, a half-blocked gully can be the gap between water draining and water pooling against your back door.
What to do: Wear rubber gloves, lift each gully grate and clear the pot below. Pour in a bucket of water, because this confirms it drains freely. Clear leaves from the downpipe outlet. If you have a flat roof, check its outlet too.
Time needed: A short time for a standard London house, since it is only a few gullies.
Check 2: Check Your Inspection Chamber
If you have an inspection chamber in your garden, courtyard or front path, open it and look inside, since you are checking two things.
Is it flowing freely? In dry weather you should see a trickle in the channel, or no water. While standing water that does not move suggests a partial blockage downstream, and storm flow will make it worse.
Is it silted? Because silt in the channel narrows the drain, if you can see a clear build-up, clear it before the storm.
If the chamber is full or overflowing before the storm arrives, you need a professional at once, since the next rain will make it worse. Request a quote online via our contact form.
Check 3: Test All Internal Drain Points
Run cold water from every tap for a short time and watch how fast it drains, because slow flow is a warning. Try the kitchen sink, the basin, the bath and the shower. Then flush the toilet.
What you are looking for. Watch for slow drainage, gurgling from nearby drains while water runs elsewhere, or water that backs up before it drains. Any of these points to a partial blockage that will worsen in a storm.
Gurgling matters most, since it means the drain is under pressure from flow downstream, or that air is being pulled through the system. A drain that gurgles in dry weather may back up fully in a storm.
If a fixture drains slowly the day before a storm, call a drainage contractor at once. Do not hope it clears itself, because clearing a partial blockage early is far less disruptive than a sewage backup during the storm.
Check 4: Know Your Flood Risk Before the Storm
The Environment Agency and the Greater London Authority map London's flood risk in detail. Checking your own risk takes minutes, and it helps you choose which checks to do first.
How to check, since it is quick.
- Visit the Environment Agency flood risk maps on gov.uk
- Enter your postcode to see your risk from rivers, sea and surface water
- Focus on surface water risk, since it matters most for most London homeowners
Homes rated high or medium for surface water flooding are the most exposed in a storm, so if yours is one, the checks above matter even more.
It also helps to know the type of risk. Surface water flooding happens when drains cannot take the rain fast enough, so water runs over the ground. Sewer surcharge happens when the public sewer backs up into homes. Clear gullies reduce the first, while a non-return valve is the answer to the second.
Check 5: Prepare Emergency Access to Your Isolation Points
If flooding does happen despite your care, you need to know how to shut off water, power and gas, so learn this in advance.
Water stopcock. It is usually under the kitchen sink or in the airing cupboard. Know where yours is and check that it turns, because a seized stopcock is a real problem in a flood.
Fuse board. It is usually in the hall, under the stairs or in a cupboard. Know where it is and how to switch off single circuits, since if floodwater reaches any electrics, switch off that circuit at once. Do not restore power until an electrician says it is safe.
Gas meter and valve. It is usually in the meter box on an outside wall or in the basement. Because floodwater is a risk near gas, if flooding is close, turn the valve off.
What to Do During the Storm
Because speed matters, if water starts rising during the storm, follow these steps.
- Do not flush toilets or run taps if internal drains are backing up, because this adds to the problem
- If surface water rises towards your door, put up any flood barriers or sandbags you have
- If sewage is backing up, leave the area and call for emergency drainage help
- Watch the external chamber, since if it fills to the top, the public sewer is surcharging and you should tell Thames Water as well as your contractor
Since storms bring emergencies, see our emergency drain service page for flooding emergencies. For storm callouts, request a quote online via our contact form.
What We Learn from Each Storm
Every named storm changes the plan a little. After wet winters, gully clearance has often belonged ahead of chamber checks. Surface flooding has often traced back to gullies clogged with leaves from the autumn before. After summer thunderstorms, the soil-stack vent check is worth adding, because some problems trace back to vents capped during loft conversions. These only fail under the high flow that storms bring. One pattern repeats. Homes that flooded once in a sewer surcharge often flood again in the next similar rain, unless a non-return valve is fitted.
If your home has a history of storm-related drain trouble, the most useful step is an off-season CCTV drain survey, because it sets a baseline for your laterals and finds partial blockages before the next storm. Homes on combined sewers, which covers much of inner London including Camden, Islington and Lambeth, can also gain from our autumn leaf-fall drain guide and the warning signs of a blocked sewer.
Frequently Asked Questions
How much rainfall does it take to overwhelm London's drains?
London's drains were designed for a certain level of storm, although named storms can exceed it. Surface water flooding tends to start sooner in areas with lots of hard surfaces. The more hard ground, the less rain it takes.
Will clearing my gullies prevent flooding if the public sewer surcharges?
Not entirely. Clear gullies cut surface water flooding because they let in the most water. Yet they do not stop sewer surcharge if the public sewer itself is full. The two problems need different answers. Clear gullies help with surface water, while non-return valves help with surcharge.
Is a non-return valve worth installing before a storm?
It is not a last-minute fix, since we quote each fitting individually. Even so, it is a lasting protection worth planning if your home has had a sewer surcharge before.
What should I do if I think a public sewer is surcharging into my property?
Report it to Thames Water, since it looks after the public sewer. Alongside this, contact our team via our contact form for emergency drainage support at your property.
Can you attend during a named storm event?
Response times can be longer during peak storms because demand is high across London.
Because every property is different, start with our guides to emergency drain services and pre-purchase drain survey advice. We also cover emergency drain services in Tower Hamlets and emergency drain services in Wandsworth, so you can see how the work runs near you.
