last updated September 26th, 2025
Floodplains and flood risk are often mentioned when buying a property there many types of flooding that can happen to a home. As it is the most dramatic, it gets most news coverage there are other common types of flooding to homes.
When we look at a house, we have two types of water leaving the property - 'surface water' which is rain and 'foul water' which is sewage. Sometimes rainwater from your roof enters the gutters and discharges from a rainwater pipe into a 'local' drainage system on your property termed a 'soakway' - in simple terms it is a hole in the ground filled with stones and usually covered by soil. The water accumulates underground and 'soaks away' slowly as it rains.
In other cases, the rain water connects to a local surface water drainage system that empties into local streams and rivers. This water is untreated as it is almost pure water. You are charged a small amount by your water/sewerage company for this service. The house sewage will also travel in a separate pipes to your local treatment plant where it is treated and discharged into a local stream or river.
There is also a third case where the rainwater system joins the sewage pipes and the 'combined' water is treated locally as sewage waste.
It is increasingly common for periods of intense rain to cause flooding. Part of the reason is that we have 'concreted over' many areas of green including lawns in front of houses for parking. Instead of the rain draining away slowly through the grass, it immediately flows onto the street and overloads the roadside drainage systems. Add the intensity of building that we see in some areas and the fact that many main drain pipes underground have not been increased in size and we have obvious floods. The pipes cannot carry the water away quickly enough, the streets flood over and you may manhole lids lifting. If you have a surface water manhole beside a sewage manhole, you may get water entering the sewage system. If the ground is heavy clay, you can also have 'ponding' with the water remaining long after the rain has stopped.
If we have a combined rain/sewage water system and it rains, the pipes can again flood over but this time it is diluted sewage that appears on the streets.
If you have a basement toilet, shower or kitchen where water can enter the sewage system, you should be aware of this risk as you can gave diluted sewage coming out of your basement waste pipes. 'Non-return valves' which prevent this happening by closing the pipe when water tries to come up the pipe can reduce this risk but they are not 100% reliable.
If there are springs near or under the house, heavy dampness on lower bricks below the Damp Proof course (see House Buyer Tips - Where to check for water damage and dampness in a home survey) may be visible or the owner may have installed a 'French drain' around the house (a hole is dug around the affected area close to a wall and filled with small stones / shingle). These can be very successful at stopping dampness but if you see water coming out of air bricks especially after rain, there is a serious problem. To check, put a small inspection camera (they are cheap and can connect to a mobile phone) through the air bricks and see if there is a 'pond' under the house. If a house has had any of the downstairs flooring changed, always ask the reason - it could be dampness.
If you live near a body of water such as a river or canal and your building is only a few metres above 'normal' water levels, you can expect flooding sooner or later as heavy rains or storms will cause water levels to suddenly rise - this will usually be reflected in high insurance premiums.
As it is the most dramatic, it gets most news coverage so always check local news websites for stories on flooding. Check Government sites for information on 'river, sea, groundwater and rainfall levels' as these have historical information and are up to date.
As building develops, diverting waterways underground in to a 'culvert' (an underground pipe) is increasingly common. If during flooding, the pipe cannot cope with the increased volumes of water, there will be flooding at the entry to the pipe. Always get a check on flood risk from your solicitor before you buy and get plans on any culverts.
Snow thaws to water and although it is gradual, it often causes localised flooding - always keep the gullys and gutters in your property clear of leaves to have good flow. Frozen pipes both internal and external can cause flooding when thawing - internally it is usually in attic or in sheds and externally it is uninsulated taps that are at risk.
As a general rule, if water flows 'naturally' from a neighbours ground onto your property, you must accept it and ensure that it causes no damage to you. You cannot simply pipe it away and flood your neighbours! However, if a neighbour installed land drainage pipes on their land and then emptied the water from the pipes onto your land you can take legal action as the water flow is no longer 'natural' but man-made. When buying a house, this can be the source of a dispute as outlined at Buying a home - are you buying a property dispute?.
Unfortunately, it is not unknown for builders to connect the pipes in a home to the wrong street pipes with the result that you get sewage in a rain-water pipe and rain in a sewage pipe. It is fairly easy to remedy.
Think carefully about living directly below any waste/water storage system or a reservoir however small it may be - failure can cause catastrophic damage.
