The guardians of Guernsey's water: how the water quality team safeguards public health
The presence of metamitron at Longue Hougue Reservoir was discovered through one of more than 25,000 routine water quality samples taken each year, which undergo laboratory analysis for nearly 180 different chemicals.
In 2024, Guernsey Water supplied 4,395 megalitres of treated drinking water through its three Water Treatment Works. This water was transferred to four Treated Water Service Reservoirs and delivered to customers via more than 420km of potable water mains.
Ensuring the safety and quality of Guernsey's water is the job of the six-member Water Quality Team, led by Water Quality Risk Manager, Daffyd Griffiths. This dedicated team carries out careful monitoring and testing at every stage of the water supply process - from natural sources right through to customers' taps. They also work on improving treatment methods, helping to prevent and clean up pollution (in partnership with the Office of Environmental Health and Pollution Regulation), working with local landowners and stakeholders, engaging with the community through education and outreach, and exploring new technologies to keep our water safe now and in the future.
On a daily basis, the team checks for bacteriological and chemical quality in line with the UK Drinking Water Regulations. Testing is carried out at three stages, the water treatment works, the service reservoirs and directly at customers' taps.
The team also routinely monitors 18 streams to help identify the best-quality sources, minimising risk and improving cost efficiency of treatment processes. In 2024 alone, 15,000 tests were carried out on stream and stored waters, targeting substances such as nitrates, pesticides and PFAS.
Routine testing covers 128 different pesticides and 48 different PFAS compounds. If these are detected, the team works collaboratively with landowners, farmers and organisations such as the airport to promote best practice and pollution prevention as part of targeted catchment audits.
In addition to treated water, the team monitors the quality of raw water from Guernsey's 14 reservoirs. These are where water is stored before undergoing clarification, filtration and disinfection at one of the island's three treatment works: St Saviours, Kings Mills and Juas.
Mr Griffiths said; "The majority of operational monitoring sampling is of raw water and goes to the UK for pesticide and PFAS analysis. This is all part of the 'source selection' methodology to ensure we collect water of the best quality from the sources that are available. This requires careful consideration as it is also vital to ensure that we have enough water to supply the island through the warmer, drier times of the year.
"Safe drinking water plays a vital role in protecting the health and wellbeing of our island. Ensuring a reliable, resilient, and high-quality supply of drinking water is Guernsey Water's top priority - not only a core part of our business plan but a commitment that shapes the daily work of every one of our colleagues."