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Cleaning our Water

Having access to clean drinking water is vital for human health. Thanks to the water treatment we have in today’s society, we’re able to drink water that is of the highest quality in the world. To do this we need to kill bacteria and remove dirt and certain chemicals (like pesticides and herbicides) to make the water safe to drink.

In the agricultural world, reducing pests using pesticides and herbicides is common practice to help grow healthy crops.  However, rainfall can cause these chemicals to run off fields and into rivers, ditches and streams contaminating the raw water.  This means it either requires intensive treatment and processing before it is safe to drink, or it exceeds the European limits for pesticides in drinking water.

Metaldehyde is most often used amongst farmers as a way to stop one of the most damaging pests around - slugs. And while this works well for farmers as a way to ensure these pests don’t ruin their crops, the knock on effect is metaldehyde being found in our watercourses and reservoirs - and removing it from our drinking water is costly, time consuming and carbon intensive.

While metaldehyde is not harmful to human health at the low concentrations it occurs in water, ridding water of the chemical cannot be achieved through conventional treatment, and is almost impossible – requiring exorbitantly expensive, carbon intensive processes.  

Putting in additional treatment isn’t an option for two reasons. Firstly, it doesn’t exist on a scale sufficiently large enough to be able to treat the quantities of water needed in the East of England, let alone the whole of the UK. Secondly, it’s extremely expensive and water bill-paying customers would be expected to pay for the additional treatment equipment. In the Anglian region alone it’s estimated that such treatment for metaldeyde would cost £595million to construct and see customer bills rise by as much as 21%. Customers would potentially then incur further costs to cover the bills for running the new equipment.

UEA was approached by Anglian Water to help find a more cost effective and sustainable solution to the use of metaldehyde, and look at how levels of the pesticide in rivers and reservoirs could be brought below the strict European standard of 0.1 micrograms per litre (or parts per billion) in treated water - the same as two grains of sand in an Olympic sized swimming pool. 

Dr Ruth Welters from UEA’s School of Environmental Science, along with Professor Brett Day and Dr Greg Smith, now at the University of Exeter, worked with Anglian Water to develop the ‘Slug it Out’ programme - the largest example of a agri- product substitution campaign that has ever been tried in the UK.

In autumn 2015, Slug it Out was launched. Farmers uses ferric phosphate for slug control, instead of metaldehyde, in the natural catchments of six reservoirs in Northamptonshire, Suffolk, Essex and Cambridgeshire. The properties of ferric mean it is equally suitable as a pest control chemical yet more sustainable and not as readily soluble in water as metaldehyde, and so less likely to end up in watercourses when it rains.

The first year of the trial saw 89 farmers sign up to take part – a 100% uptake. The trial area covered 7,679 hectares and an estimated 1,613 kg of metaldehyde was removed from the farmed landscape bringing down the average levels of metaldehyde in reservoir tributaries across all the catchments by 60%.

The trial has now been extended for a second year in the same six catchments, plus Rutland - the largest natural catchment in the UK and covering 7,500 hectares - effectively doubling the trial’s hectarage. Once again farmers in these areas will be asked to agree to use alternative slug control options to metaldehyde on their land. This will allow researchers to verify their findings over an even larger farmed area and time frame, building on their evidence base and helping to identify the package of measures needed.


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Dr Ruth Welters

Senior Research Associate, School of Environmental Sciences

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