Scottish Water expands publication of 2025 overflow event data

“With this release of annual data from an additional 1,009 monitored locations, we are giving a much fuller view of how our sewer network is operating.”

Simon Parsons
Director of Wastewater, Scottish Water

Scottish Water has published annual overflow event data for 2025 from over 1000 additional monitored locations across Scotland, delivering the next stage of its commitment to make more information on wastewater overflows publicly available.  

Overflows are designed to protect homes, businesses and communities from flooding during periods of heavy rain. ‘Event duration’ monitors indicate when overflow events occur and record when they start and stop.  
 
Today’s publication expands on the number of locations monitored, giving communities across Scotland access to data on how our overflows have operated during 2025.  The number of recorded overflow events is higher than previous years – as the report reflects the much larger number of overflows included.   

The additional monitors form part of Scottish Water's £500m Improving Urban Waters programme, which is increasing monitoring and transparency, and supporting action to improve the water environment. 

The August update means: 

• New published data takes the total number of monitors with annual published data available in Scotland from 6% to 30% (1287). 
• Over 4.5 times more data locations are now available. It shows four times as many overflow events occurring and less than double the duration of events. 
• On average our monitored overflows operated 2.5% of the time in 2025.
• Almost 20% did not operate at all during 2025.   

This new information will help Scottish Water better understand how rainfall impacts our sewer network and, where needed, make better-informed decisions about where improvements can provide greatest environmental benefit.

Scottish Water will continue adding monitors to its near-real-time map and plans to publish annual 2026 overflow event data for all locations shown on the map in March 2027.

Scottish Water Director of Wastewater Simon Parsons said: “We made a clear commitment to publish more information about overflows, and with this release of annual data from an additional 1,009 monitored locations, we are giving a much fuller view of how our sewer network is operating.

“It is important to understand that a larger dataset will contain more recorded events. That does not in itself mean overflows are operating more often. It means we are now making information available from many more locations.

“This greater visibility will help us investigate performance, understand where the network may be affecting the environment and target action and investment where it can make the most difference.” 

Additional Information

Around 99% of the wastewater discharged from sewer overflows when there is heavy rain is rainwater and ‘grey’ water from households and appliances and not sewage, so any risk to environmental harm is minimal. 

SEPA's River Basin Management Plans set out the range of factors that impact overall water quality classification. 

Over and above the monitoring of overflows, SEPA independently tests water quality across Scotland and as things stand 87% of all water bodies are considered as being in good or better condition.  

New Event Duration Monitor (EDM) installation has been based on the agreed prioritisation with SEPA, our environmental regulator, targeted to deliver the highest levels of protection and the most significant benefits. 

The accompanying data and user guidance explains the coverage, data availability and recording approach so that the figures can be understood and interpreted appropriately. 

The publication also includes all available overflow events for the additional locations, including shorter-duration events. Previous annual publications generally included overflow events lasting more than 15 minutes and 30 seconds. This more comprehensive approach will apply across all overflows for the publication of 2026 data. 

More than 2,000 locations are now shown on Scottish Water's near real-time overflow map.