Storm overflow map
This map provides near real-time information about Dŵr Cymru’s storm overflow activity, as indicated by our event duration monitors.
Please note that this is a beta version of the storm overflow map. We are using this version to continue to test and improve the site.
or you can view the map in a new window.
How to use the map
Each of our storm overflows is represented by an icon. When you click on an icon, a pop up appears which gives information about the operating status of the storm overflow.
What do the different icons mean?
The legend widget on the right-hand side of the map shows the meaning of the different symbols – with the different colours and graphics representing the status of the storm overflow.
There are two types of overflows. Storm overflows are represented by circular icons and overflows are represented by triangular icons. The overflows represented by triangular icons are currently operating as storm overflows but are not designed to do so in the long term. These are currently under review.
There are four types of status for each overflow, with the different graphic infills and colours reflecting the spill status.
How do I find my location on the map?
There are three ways of finding a specific location on the map.
- You can use the search widget to search for an address or area.
- You can use the find my location widget (if device settings are enabled) to automatically find and zoom into your location. This feature is very useful if using a mobile device.
- You can also zoom in and out of the map using the + and - buttons
You can also use the basemap widget to switch to a different basemap (background map) view.
To return to the default map view, click on the home button.
You can use the layers widget to switch on/off different layers such as bathing water areas, just leaving the storm overflow asset info, if required.
How do I know if a storm overflow is operating, or not?
Clicking on the asset pin enables a pop-up. This pop-up contains information about the asset – including whether it is currently operating or not and the date / duration of the last storm overflow event.
About Storm Overflows
What are storm overflows?
You can learn more about storm overflows here.
About Event Duration Monitoring
What is EDM?
EDM stands for Event and Duration Monitoring. We report EDM data for each asset annually to our environmental regulators, following an industry- wide standard called the 12/24 methodology. We also upload our annual data set to our EDM map, on our website. You can read more about EDM here.
Frequently asked questions
We are communicating our ‘near real time’ information to customers in the way we receive it directly from the asset, meaning it has not been cleansed or validated. This does mean there may be some discrepancies, which we are always looking to improve on. But it does mean our data will be visible to you, as we see it.
As is the case with the other water companies, the information we display on the near real time map is different to the EDM data we report annually to our regulators. We are aiming to report storm overflow events as quickly as possible (within an hour of operation) which means that we can’t process them into our normal 12/24 hour block counting method. A storm overflow may start and stop operating multiple times during a day in response to the same rainfall event and so we would usually group these together in a method agreed with our regulator. You can find out more about the 12/24 methodology here.
Our monitors will send information every 15 minutes however this then has to be fed into a system before it can be displayed on the map. This therefore does mean there is a slight delay between the information being received and it being displayed on the map. We can assure people however that we have worked hard to ensure the map displays the information as quickly as possible. We will of course keep this part of the process under review and speed up the process for the information to be displayed on the map if we can.
This means that our EDM monitor indicates that this storm overflow is operating. However, the volume or strength cannot be determined.
The data shared via this map is as we see it. To ensure we are open and transparent with our data, we will not undertake any validation of this data before sharing. This does mean there may be some discrepancies from time to time, which we are always looking to improve. We will endeavour to correct any information that is not accurate as soon as possible.
If we do notice any discrepancies within the source data sensor readings, we will investigate as soon as we can to establish what is causing the discrepancy so that we can correct as soon as possible.
The ‘under maintenance’ label will appear when we don’t receive data from the fixed monitor for 4 hours (or 24 hours for remote monitors), when we are aware that it produces inaccurate data, or if we identify another issue. We aim to investigate and take action as soon as possible to get the monitors working again. There are many reasons that this could happen – sometimes the monitor needs to be replaced or there could be something obstructing the monitor. They are very sensitive and something as small as a spider web can sometimes affect them. Additionally, some sites rely on phone signal to transmit information, and these can drop out from time to time. We are working hard to improve sites with poor signal across our asset base.
We don’t have the processes to be able to provide commentary on the under-maintenance status within the hour but may be able to do in the future. However longer-term issues on assets can be shown on the asset notes.
This depends on the type of issue – some can be resolved quickly whereas others will need more detailed investigation and work. We will endeavour to return any faulty monitors to reporting status as soon as possible. Where we have investment plans in place through our Storm Overflow Improvement Programme or long-term outages, we will endeavour to include this as a comment on the asset to be viewed via the map.
Bathing waters are designated bathing sites which are monitored and classified by Natural Resources Wales for water quality. You can learn more about NRW and Bathing Waters here.
When we first launched the map on 1 February 2024, we started with the assets closest to bathing waters and within 1km of swim locations from our swim survey, as well as shellfish waters. This is because our customers highlighted these were the most important assets to them and this also met our regulatory commitments. We are incrementally adding more assets and all 2,300 of our overflow assets will be live by March 2025.
To find out if a storm overflow near you is operating, you can use the ‘find my location’ feature or type your postcode or address into the search button. When you land on the location you will be able to view the storm overflows nearby and be able to check their status.
Not currently, but we are developing and testing a notification system for the map where you will be able to subscribe to receive alerts about assets. We aim to launch this by end of March 2025.
We don’t currently have the function to download the data from the map but are working on this. We hope to have this available later this year. It’s also worth noting again that the information on the storm overflow map is not the same as the current annual EDM regulatory data that’s available on our website.
The quality of a designated bathing water is classified using levels of bacteria in the water. Beaches and other open water bodies always have a level of bacteria present. Sometimes, coming into contact with certain bacteria can make people unwell. These bacteria are very common and can come from many sources including wastewater, privately owned sewer systems, misconnections, run off from both urban and rural areas, livestock, birds and even pet dogs. Where a bathing water has a lower classification than Excellent, Welsh Water may need to investigate our nearby assets, which can be a very complex process.
Our Storm Overflow platform is being progressively delivered and our map currently shows overflows within a certain distance from a measured location. These include;
- within 1km of the Urban Wastewater Treatment Directive sensitive areas (bathing waters)
- within 2km of a Natural Resources Wales bathing water monitoring point
- within 1km of popular non designated swimming locations identified by our 2023 swim survey
Storm overflows do not necessarily impact bathing water quality and equally, the absence of a storm overflow operating does not guarantee a particular quality of bathing water. Identifying the source of bacteria can be very complex and challenging but we work closely with relevant organisations to help improve our operations where assets may contribute.
Natural Resources Wales’s Bathing Waters webpage includes a profile of each designated bathing water in Wales. This includes sample data, catchment area descriptions, agricultural inputs, as well as water company information .
We cannot advise on bathing water safety or quality. This platform is a tool which gives water users information on the operation of our storm overflow assets. We want our information to be accessible for water users to be able to make an informed decision before entering or using the water. This should not be considered as advice on bathing water quality. For information on bathing water quality, please refer to Natural Resources Wales’ Bathing Water pages.
Local authorities work with Dŵr Cymru Welsh Water, NRW and other influencers of water quality to determine if there is a risk to bathing. In these instances, advice and mitigation is a decision for the relevant local authority.
During periods of heavy rain, we have permits from our regulators for storm overflows to operate to prevent homes, businesses, and communities from experiencing wastewater flooding. This can happen during the bathing season because even during the summer months, the effects of climate change mean we now can see heavy and intense rainfall events at any time of the year. It is worth adding that around 95% of what is released from storm overflows is mostly rainwater and there are other factors which can impact bathing water quality aside from storm overflows. If we do identify a storm overflow that is operating more than it should, then we will investigate to understand the cause.
Natural Resources Wales – bathing water quality
Public Health Wales – Staying Safe in Outdoor Waters in Wales.
We are investing significantly to improve storm overflow performance, with £140m being invested between 2020-2025 and a further £420m planned from 2025 to 2030. You can read more about our investment plans here.