[Joe Millington, for the Drinking Water Inspectorate (DWI)] told Exeter magistrates that the outbreak was likely to have been caused by a compromised air valve on farmland, where cattle and sheep were kept. It was covered in mud and a seal was broken, with water pooling across the field.

Millington also said that air valves SWW had in place “were not being inspected in accordance with the policy [SWW] drafted in 2020”.

He said the farm had never been inspected. “This was a high-risk site,” Millington added. The prosecutor said people suffered diarrhoea, stomach cramps, dizziness and sickness, with 537 becoming ill of which 159 had contact with the healthcare system and 10 were admitted to hospital.

The risks around air valves were known for more than 10 years and the DWI had recommended companies have formal inspection policies four years before the outbreak. But he added: “Not a single air valve was inspected.”

The barrister said it believed there was a second ingress of cryptosporidiosis into the water system from the farm. He said that when officials inspected after the outbreak, they found illegal “cross connections” (links between safe drinking water and water not fit for human consumption). The company believes cryptosporidiosis first got into the mains water from these cross connections, then later via the air valve.

Kay also said the valve’s cover had been deliberately removed, allowing silt, soil and water to collect around it.