London sewer flooding prevention

We want to find the properties that are at higher risk of sewer flooding and take action to lower the risk of this happening again in future. Sewer flooding happens when the sewers are overwhelmed by heavy rainfall, and wastewater from the sewer backs up inside a property–coming up through toilets, sinks and showers. The storms that cause this are rare but may happen more in the future, so we want to protect our customers as much as we can.

The survey will tell us:

• how your property is connected to the sewer
• how many sewer connections it has and whether they are shared with other properties
• which sewer/s it connects to and the size and depth of the sewer connections
• the type of property and how much of it drains to the sewer

Along with the flood history from you and your neighbours, we'll use the information to understand the risk of your property flooding in the future. If we think the risk is high enough, we’ll install a device to reduce the risk. The survey also helps us identify the best type of device for you.

We’ll install a one-way valve in the property’s sewer connection that will significantly reduce the chance of wastewater backing up into your property. If there is a risk to life or an even higher risk of flooding, we may install a one-way valve with a pump, known as a FLIP. We'll need the property owner's permission to install some devices, so if you don’t own the property please contact the owner to discuss this.

We also need to understand the risk to other properties in your neighbourhood, so when we’ve completed the surveys in your area, we’ll contact you to arrange to have a device installed if needed. This can take three to six months, depending on the device needed, whether we need permission from the local authority or highways agency and whether a combined neighbourhood solution is required. Our aim is to install devices in most higher-risk properties by the summer of 2024. We'll be prioritising those that would need the most support in the event of a flood.

You might not qualify for a device because:

• The flooding to your property was caused by surface water run-off from the roads and not by our sewers backing up inside your property
• The flooding to your property was caused by blockage or inadequate capacity of your private drains
• Your basement has been converted from a storage area to habitable accommodation after 2002. Under Building Regulations the owner of the property at the time should have undertaken a flood risk assessment and carried out appropriate measures. We’ll check the publicly available Building Regulations consents to see if any alterations were made to your basement property.

Having a sewer flooding resilience device alerts buyers to the risk of flooding. However, you’re legally obliged to inform purchasers of any issues, including flooding. So, with your agreement, your buyer can be given advice by Thames Water and the opportunity to continue to benefit from the device.

We’ll assess the risk of your property having sewer flooding in the future and offer to install a device if we believe this risk is higher. Your insurer may or may not allow for this in the scope of your insurance cover. If they don’t, we recommend you shop around, starting with insurers who are part of the Flood Re Scheme.

You can get in touch with us on 0800 316 9800 and quote reference 147944,or you can email us at consultations@thameswater.co.uk