A ban on the amateur use of glyphosate products came into effect locally in January 2023.
The utility’s annual Water Quality Report showed this quickly had an impact on water being collected.
‘Pesticide sampling in 2023 identified a decrease in average glyphosate concentrations in streams and reservoirs by approximately half compared to the five-year pre-ban average, with more densely populated northern catchments in particular decreasing by a significant magnitude,’ said the report, which covers 2023.
‘These initial results support the water quality reasoning for the introduction of the ban. However, it will be important for Guernsey Water to continue monitoring for glyphosate in the years to come, as well as for other pesticides should islanders seek to use alternative products.’
The 2024 report is currently being prepared. Guernsey Water has been urging islanders to be more cautious with their water usage in recent weeks. Reservoirs are just below 90% full, but are falling after inconsistent rainfall in recent months.
Rainfall for the year to date has been below average.
The raw water collected is closely monitored to safeguard the quality of drinking water, with testing carried out on streams and raw water reservoirs.
‘The results of these analyses allow us to select which streams we collect and when, to minimise the risk to stored water before treatment,’ said Guernsey Water.
‘As the impacts of climate change and increasing demand for water from future customers manifest it will be essential to continue to monitor and act upon the results of raw water pollution to maximise volumes available for collection.
‘Regulatory changes around pesticides and PFAS substances are also likely to require additional monitoring and risk management to ensure continued compliance.’
PFAS substances, such as perfluorooctane sulphonate or PFOS, which was historically used in firefighting foam at Guernsey Airport, have been monitored regularly in Guernsey since 2007 to track historic contamination of several catchment areas in the south of the island.
Guernsey Water has been working with the director of Environmental Health & Pollution Regulation and other States departments to reduce PFOS levels found in raw water by treatment of stream water from affected catchments, removal and containment of contaminated soils, and construction of stream divert structures to enable source selection. It has had some success and the efforts will continue.
Guernsey Water has three water treatment works and four service reservoirs. In 2023 it was found that Juas water treatment works had been fully compliant with prescribed limits, while St Saviour’s and Kings Mills had each exceeded the limit once.
Both involved instances where the ‘turbidity parameter’ – a measure of the cloudiness or haziness caused by suspended particles – was exceeded, but this had not impacted the microbiological or chemical quality of the water.
At the treated water service reservoirs Forest Road west, east and tower each exceeded levels once, due to a single coliform bacteria.
The report did note that nitrate levels in some streams were at the upper acceptable limit, but through careful blending and storage, levels are reduced to ensure compliance with the prescribed limit.
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