South West Water is explaining why a storm overflow alert can sometimes appear on its Water Fit Live web page even when no spill has taken place.
The company has seen a number of recent alerts which, following investigation, were found not to have been caused by storm overflow spills and wants to help customers understand why this can happen.
Helen Dobby, Head of Environmental Performance at South West Water, explained: "People understandably assume that a storm overflow alert means a spill has taken place. In the vast majority of cases that's exactly what it means, but occasionally we investigate an alert and find it was triggered by something other than a discharge."
Storm overflow alerts on WaterFit Live are generated by Event Duration Monitors (EDMs), sensors installed at storm overflow locations that detect when a spill event starts and stops.
Most alerts from EDM's reflect genuine storm overflow activity but alerts can occasionally be caused by debris and obstructions, or by sensors and telemetry systems not working correctly.
These issues can be complex and take time to diagnose, meaning an alert can sometimes appear on WaterFit Live even though no spill has taken place.
This happened recently in Falmouth, where an alert was investigated and subsequently confirmed to be false, with no spill having taken place.
Once the investigation was complete and the EDM was found to be faulty, further non-genuine alerts from that monitor were suppressed until the issue was resolved.
Helen said: "We want customers to have access to the most accurate and up-to-date information possible. If our investigations show that a spill hasn't taken place, we update WaterFit Live to reflect those findings and take steps to prevent further incorrect alerts while the issue is resolved."
South West Water publishes storm overflow alerts in near real-time because it believes customers and water users should have access to information as quickly as possible.
"We believe water users should be able to see information from our monitors as quickly as possible,” Helen said. “Because the data is shared in near real time, there may occasionally be occasions where an alert appears before we've completed all our checks. In a small number of cases, further investigation may show that no spill has actually taken place."
The company also provides this monitoring data to organisations including Surfers Against Sewage (SAS), which uses the information in its Safer Seas & Rivers Service.
Alerts are shared with SAS at the earliest opportunity to help provide near real-time information to water users.
If an investigation later confirms an alert was not caused by a spill, South West Water updates WaterFit Live and shares the corrected information with organisations that use its data, including SAS.
As a result, information displayed on different platforms may occasionally vary depending on when updates and corrections are processed.
South West Water minimises the risk of displaying non-genuine alerts through regular maintenance and calibration of its monitoring equipment. Its EDM operability is currently 96.7%, across its 1,361 storm overflows, which is the second highest in the industry and well above the industry average.
The company is looking to improve further and is also exploring ways to identify false alerts more quickly, including through additional sensors and improvements to its IT systems.
Helen added: "We recognise that false alerts can be confusing for customers, which is why we're continuing to invest in monitoring equipment, sensors and technology to help us identify and correct them as quickly as possible."
For more information about how South West Water uses and shares its storm overflow data visit the Storm Overflow Data page
To view South West Water’s storm overflow map visit Storm overflow map | WaterFit Live | South West Water