An overview of the alerting method used in each water company region

There is currently no national standard for sewage alerts. The process of turning sewage discharge data into a warning on the Safer Seas & Rivers Service (SSRS) app varies depending on which water company region the alert is issued in, because each water company uses a different method to assess how sewage affects bathing waters.

This patchwork system across the sector is why we have been part of a national programme to create a standardised alert that accurately determines whether sewage discharges are affecting the water. The results of that programme have shown that water companies are failing to produce suitable alerts, which is why we will continue working behind the scenes to ensure the information you receive is useful, accurate and keeps you safe.

In practice, the differences fall into a few broad categories:

• Impact modelling. Most water companies have no model at all, so the true effect of a discharge on water quality is largely unknown. Only Anglian Water, Southern Water and South West Water currently run predictive models, and none of these models is official guidance.

• Mapping. Which overflows are linked to which bathing waters is usually decided by the water company itself, although in some areas we use Environment Agency mapping instead.

• Thresholds. Some regions apply a minimum discharge duration before an alert is issued; others alert on any discharge.

• Duration. How long an alert stays live after a discharge ends also differs, from 12.5 hours to 48 hours depending on the region and the provider. SAS currently keeps sewage alerts in place for 48 hours after a discharge has ended as a precautionary approach. This aligns with the recommendations of the UK Water Industry Report ‘Improving real-time bathing water quality information’ project, which proposes a standardised 48-hour warning period based on scientific modelling of bathing water quality.

Across every region, SAS is calling for better assessments of how real-time sewage discharges affect water quality, so that water users receive consistent, accurate and clear advice.

We access data from Thames Water on real-time discharges from its sewer overflows, allowing us to know when a discharge is occurring and how long it lasts. Alerts are issued for bathing waters based on a mapping provided by the Environment Agency via the bathing water profiles.

There is currently no impact model in place, so the true effect of these overflows on water quality is largely unknown. Thames Water took part in the national programme aimed at improving the way real-time water quality alerts are issued, but it currently has no plans to introduce modelled sewage alerts for coastal bathing waters.

We access data from Anglian Water’s BeachAware system, which calculates the volume of stormwater being discharged alongside a coastal model that takes tidal conditions into account. The system then predicts how the overflow will affect bathing water quality. If it predicts that water quality at nearby bathing waters will fall below the ‘Good’ standard, an alert is automatically generated and we issue a sewage alert in the app.

SAS removes an alert after a 48-hour period with no further modelled impacts on water quality. Anglian Water removes its alerts after 24 hours.

The BeachAware model has not been independently verified or reviewed. It is reviewed throughout the year, with a review carried out on all activations, and a full annual review is carried out before the start of each bathing water season. This includes site tests of each of the EDM points that feed information into the BeachAware system, ensuring that the points are working as designed and that data is uploaded correctly.

The SSRS is the only place to view BeachAware alerts.

We access data from South West Water’s WaterFit Live system, which predicts how sewage overflows will affect bathing water quality. More information is available in the WaterFit Live Methodology document, which explains how WaterFit Live works and the definitions and criteria used to make decisions.

SAS removes an alert after a 48-hour period with no further discharge impacts on water quality. South West Water removes its alerts after 12.5 hours.

The WaterFit Live model has not been independently verified or reviewed.

We access data from Yorkshire Water on real-time discharges from its sewer overflows, allowing us to know when a discharge is occurring and how long it lasts. Alerts are issued for bathing waters based on a mapping provided by Yorkshire Water, which identifies the storm overflows with the potential to impact each bathing water. We apply a threshold of five minutes, meaning an alert is only issued if a discharge lasts longer than five minutes. This threshold was agreed with Yorkshire Water.

There is currently no impact model in place, so the true effect of these overflows on water quality is largely unknown. Yorkshire Water took part in the national programme aimed at improving the way real-time water quality alerts are issued, but it currently has no plans to introduce modelled sewage alerts for coastal bathing waters.

Yorkshire Water is working on a project to predict water quality at inland locations, which you can read more about on their website.

We access data from Wessex Water on real-time discharges from its sewer overflows, allowing us to know when a discharge is occurring and how long it lasts. Alerts are issued for bathing waters based on a mapping provided by Wessex Water, which identifies the storm overflows with the potential to impact each bathing water. We apply threshold times to each bathing water and overflow pairing, meaning an alert is only issued if a discharge lasts longer than the specified threshold. These threshold times are provided by Wessex Water.

There is currently no impact model in place, so the true effect of these overflows on water quality is largely unknown. Wessex Water took part in the national programme aimed at improving the way real-time water quality alerts are issued, but it currently has no plans to introduce modelled sewage alerts for coastal bathing waters.

Sewage alerts that impact bathing waters in the Southern Water region are generated by Southern Water’s Rivers and Seas Watch predictive alerts. These use tidal modelling to work out what will happen to a storm overflow release once it hits the water, and which bathing waters it could impact. The tidal model predicts release behaviour, factoring in wind, tide strength and direction.

The model has been independently reviewed by bathing water and hydrodynamic specialists, but is not official guidance. SAS is calling for better assessments of how real-time sewage discharges affect water quality, so that water users receive consistent, accurate and clear advice.

We access data from Northumbrian Water on real-time discharges from its sewer overflows, allowing us to know when a discharge is occurring and how long it lasts. Alerts are issued for bathing waters based on a mapping provided by Northumbrian Water, which identifies the storm overflows with the potential to impact each bathing water.

There is currently no impact model in place, so the true effect of these overflows on water quality is largely unknown. Northumbrian Water took part in the national programme aimed at improving the way real-time water quality alerts are issued, but it currently has no plans to introduce modelled sewage alerts for coastal bathing waters.

Sewage alerts in Scotland are triggered when a sewer overflow discharges within 2km of a designated bathing water, based on publicly available information from Scottish Water. The alert remains in place for 48 hours after the discharge ends.

Unlike other parts of the UK, Scottish Water does not assess whether a discharge impacts bathing water quality. These alerts are therefore precautionary: they show that a discharge has happened nearby, but do not confirm whether the water is unsafe.

We access data from Welsh Water on real-time discharges from its sewer overflows, allowing us to know when a discharge is occurring and how long it lasts. Alerts are issued for bathing waters based on a mapping provided by Welsh Water, which identifies the storm overflows with the potential to impact each bathing water.

There is currently no impact model in place, so the true effect of these overflows on water quality is largely unknown. Welsh Water took part in the national programme aimed at improving the way real-time water quality alerts are issued, but it currently has no plans to introduce modelled sewage alerts for coastal bathing waters.

We access data from United Utilities on real-time discharges from its sewer overflows, allowing us to know when a discharge is occurring and how long it lasts. Alerts are issued for bathing waters based on mapping provided by United Utilities, which identifies the storm overflows with the potential to impact each bathing water. There are some exceptions to this where, following careful consideration with local stakeholders and United Utilities, we have adopted the mappings provided by the Environment Agency for bathing waters in the Wirral area.

There is currently no impact model in place, so the true effect of these overflows on water quality is largely unknown. United Utilities took part in the national programme aimed at improving the way real-time water quality alerts are issued, but it currently has no plans to introduce modelled sewage alerts for coastal bathing waters.