A ban on the outdoor use of metaldehyde that is to be introduced across Great Britain from spring 2020 will ultimately benefit the water treatment process.

Environment secretary Michael Gove announced the proposed restriction to the pesticide, which is used in many slug pellets, in a bid to better protect wildlife.

The decision to prohibit the use of metaldehyde, except in permanent greenhouses, follows advice from the UK Expert Committee on Pesticides (ECP) and the Health and Safety Executive (HSE) that metaldehyde poses an “unacceptable risk to birds and mammals”.

The impact on drinking water was not a factor in the advice from ECP and HSE, but the restrictions will help water companies to avoid issues with the pesticide.

Steve Lambert, senior catchment and water quality scientist at SES Water, told Utility Week: “Ever since 2008 when improvements in analytical techniques revealed high concentrations of metaldehyde in sources of water used for drinking supplies for the first time, the agricultural community and water industry have worked together to find solutions to retaining the pesticide for slug control.

“The response from farmers in our catchment area throughout this period has been superb, so much so that concentrations in the River Eden this autumn have continually remained below the 0.1ppb Drinking Water Standard for the very first time.”

He added: “While the potential risk to drinking water was not a factor in bringing in the ban, the move will provide benefits over the longer term in the treatment process needed to ensure we remain compliant with our obligations. We will continue to work with farmers in our area on viable alternatives to metaldehyde as part of our ongoing catchment management activities to mitigate risks to drinking water supplies.”

Gove said: “I recognise that significant effort has been put into encouraging growers and gardeners to use this pesticide responsibly by the Metaldehyde Stewardship Group. However, the advice is clear that the risks to wildlife are simply too great – and we must all play our part in helping to protect the environment.

“I encourage companies and growers to look at the alternatives, such as ferric phosphate, which is authorised and does not carry similar risks.”

The outdoor use of metaldehyde will be phased out over 18 months to give growers time to adjust to other methods of slug control.

The Department for Environment, Food and Rural Affairs (Defra) said it will be legal to sell metaldehyde products for outdoor use for the next six months, with use of the products then allowed for a further 12 months.

It said: “The new restrictions on metaldehyde will also reduce the possibility of the pesticide contaminating drinking water sources. Although this was not a factor in the advice from ECP and HSE, the restrictions will help water companies continue to meet our robust drinking water standards.”