How to prepare for flash flooding

Flash flooding (also known as surface water or sewer flooding) can happen when very heavy rain falls on hard surfaces overwhelming drainage and sewers. This sort of flooding is difficult to predict, it often happens quickly with fast flowing water that could pose a risk to life. It is also more likely to happen during intense summer storms but can occur anytime of year. The likelihood of flooding remains low for most basement properties, but where it does occur, damage and risk to life can be serious.

Who to call during a flood

• For emergencies such as serious illness, injury and risk to life, call 999: fire, ambulance and police services
• If your toilet, sink or bath is flooding (e.g. if wastewater or raw sewage is coming up through your toilet, sink or bath), call Thames Water: 0800 316 9800
• Inform your council of flooding coming from outside your property e.g. from the road or pavement. First, find your local council, then find contact information for the right team by searching for ‘flood’ or ‘flooding’ through the council website.

Useful contacts

• For general advice, call the Environment Agency’s 24-hour floodline: 0345 988 1188
• The National Flood Forum has a helpline that provides general support before, during and after a flood on issues including insurance, home re-instatement and home resilience. Contact the National Flood Forum charity: 01299 403 055.
• To find an insurer, try FloodRe.
• If you are a renter add the number of your landlord, housing officer or housing association call out number to your phone. Inform your landlord/housing association if your home has flooded and needs repairs.

DID YOU KNOW: having insurance is important in case your home and belongings are damaged or destroyed during a flood. Have you checked your building or contents insurance covers flood damage?

• If you are a vulnerable person or know someone who is, sign up to the priority services registers for both power and water. This will be helpful in the event of power outages or water supply interruptions. 

You can also do your bit to help reduce the risk of flooding, encourage wildlife and support your wellbeing by changing just a part of your garden from grey to green. You can start small, even if you don’t have a garden of your own or you could join up with your community to run a community depaving project. If you already have a front garden keep it green. Paving over front gardens creates more impermeable surfaces which increase the risk of flooding.

The Mayor is currently greening London and reducing flood risk through his green space funding programme, the Green Roots Fund. The Green Roots Fund will support projects to improve green and blue infrastructure in London and its first round specifically has the theme of Clean and Healthy Waterways, reflecting the Mayor’s commitment to clean up London’s waterways, including streams rivers and canals. Funded projects will range from community initiatives to large-scale interventions and will all contribute towards making London more resilient.

The development of the London Surface Water Strategy has been led by Flood Ready London (formerly the Surface Water Strategic Group) formed in July 2022, in response to the storms of July 2021.

The London Surface Water Strategy is an ambitious vision of how London can address the real and growing risk of surface water flooding to our communities, the environment and the economy.

It builds on the work done to date in the context of the city’s unique challenges – and its unique opportunities. It sets out a series of actions and recommendations that the Flood Ready London partnership will progress  to find the best, most practical, cost-effective ways to help everyone in London, from business owner to basement renter, become flood ready.

This is being done through setting up ten Surface Water Catchment Partnerships  to cover the whole of Greater London. They will look for funding and implement practical, cost-effective ways to manage heavy rainfall, such as replacing hard landscaping with rain gardens, making allowances for storm surface water flows in new developments and empowering people to make the right decisions for them at the right time and scale.The Flood Ready London partnership, formed of the Environment Agency, London Councils, London Fire Brigade, Mayor of London, Thames Water and Transport for London with support from Thames Regional Flood and Coastal Committee, developed the Strategy through a series of consultations with London Boroughs, environment and development managers, community groups, the public and many others associated with surface water management.

Read more about the London Surface Water Strategy here.

Find out more about the work of the Mayor on the flooding pages.

The management of surface water flood risk (or flash flooding) in London is dispersed among a range of organisations with different responsibilities and accountabilities.

The Flood and Water Management Act specifies that surface water flooding is the responsibility of local authorities, designated as Lead Local Flood Authorities (LLFAs). In London this means there are 33 responsible authorities, one for each London borough and the City of London. There is no single responsible authority or agency bringing together the work of the individual LLFAs into a holistic picture for London.

The Department for Environment, Food and Rural Affairs (Defra) in Government is the policy lead for flood and coastal erosion risk management in England. New or revised policies are prepared with other parts of government such as the Treasury, the Cabinet Office (for emergency response planning) and the Department for Levelling Up, Housing and Communities (for land use and planning policy). These national policies are then delivered by Risk Management Authorities (RMAs). The RMAs relevant to London are:

• Environment Agency
• Lead Local Flood Authorities
• Water and sewerage companies
• Highways authorities.

Flooding is a complex hazard where multiple sources often interact, for example surface water, sewer and river flooding. It requires coordination between different Risk Management Authorities.

The Environment Agency officially has the strategic overview responsibility for all types of flood risk and works closely with Lead Local Flood Authorities, who are responsible for surface water and other RMAs in order to manage the risk. In the event of surface water flooding the Environment Agency will support partners in responding to this if resources are not needed for fluvial (river) or tidal flood response.

Water companies are responsible for managing public sewers. In London, Thames Water provides the drainage services and manages London’s sewer network and wastewater treatment facilities.