NI Water has appealed to all users of plant protection products — from farmers treating rushes and grassland weeds to householders tackling garden growth — to take extra care this season. The utility is urging people to prevent drips and spills when preparing, applying and disposing of chemicals, and when cleaning equipment in the yard.

The organisation said chemicals can be washed off fields after heavy rain or inadvertently enter drains during filling and wash-down, increasing the risk that plant protection products reach rivers and lakes that supply drinking water. Reducing these incidents helps protect raw water sources.

Rebecca Allen, NI Water's catchment officer, said: "Our monitoring shows MCPA is regularly detected in watercourses between April and October, the main application period. We know farmers are spraying rushes and weeds in grasslands now, and domestic users are treating garden weeds, often with MCPA-based products.

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"MCPA, a broadleaf herbicide, is particularly problematic for local water quality because it dissolves easily and persists in surface water, making its removal both difficult and costly to remove during treatment. Despite these obstacles, NI Water is committed to removing such substances to provide safe drinking water and meet current drinking water standards."

She added: "Losing MCPA from fields not only represents wasted expense for farm businesses, but also threatens the water environment and the wildlife it supports. It's vital that everyone works together to safeguard our valuable drinking water."

NI Water is part of The Water Catchment Partnership — which includes the Ulster Farmer's Union, DAERA, CAFRE and the Voluntary Initiative — working since 2013 to tackle pesticide pollution in raw water. While progress has been made in reducing MCPA levels, further action is still needed.

Recent measures include the 'Rush Solution Without Pollution' trials in counties Armagh, Tyrone, Antrim and Derry~Londonderry, offering free weed-wiping to more than 300 farmers as an alternative to traditional MCPA boom spraying.

In the Derg catchment, the Source to Tap Pilot Land Incentive Scheme — jointly funded by the EU INTERREG VA Programme, DAERA and DHLGH, and managed by SEUPB — provided 100% funding for weed wiping upstream of Water Treatment Works, leading to at least a 25% reduction in MCPA in raw water.