Agriculture is the number one water polluter. Livestock production pollutes our groundwater, streams and rivers directly through manure and slurry and indirectly through the pesticides used on feed crops.

Demand for animal feed is one of the major reasons behind the intensification of crop production. It is estimated that over 4.5 billion litres of pesticide are now used annually in the UK. [1] The harmful environmental effects of pesticide use are now well documented. They can affect wildlife populations - from beetles to songbirds - and many are also deemed detrimental to human health.

However, pesticides are only part of the problem. The Department for the Environment, Food and Rural Affairs (DEFRA) estimate that every year UK farmers spread about 80 million tonnes of animal manure on the land. [2] Dairy cows produce 57 litres of excreta every day. [3] The global figure for waste from industrial livestock systems is in the region of 8 billion tonnes per year. The number of industrial systems is increasing by 4% per year, a rate that will bring the total waste from industrial systems alone to 20 billion tonnes by the year 2020. [4] As industrial livestock systems are increasingly separated from the land on which crops are grown, much of this waste is not even returned to the land as fertiliser. Its storage and disposal represent a very considerable environmental hazard.

Animal slurry can be up to 100 times more polluting than raw untreated domestic sewage. Silage effluent (the liquid produced when preserving crops harvested while they are still green so that they can be kept for fodder) is even worse - up to 200 times more polluting. [5]

Manure contains high levels of nitrogen and phosphorus. These elements can leach into groundwater and run off to pollute lakes and waterways, where they encourage algal blooms that block sunlight and encourage bacteria which deplete the water of oxygen, in the worst cases killing all the fish and endangering the health of other animals in the area. This process is known as eutrophication, and farming is the major cause.

Slurry, which is made up of manure and urine, contains high levels of ammonia, which can adversely affect plant growth and contributes to acid rain, further damaging water and air quality and contributing to loss of biodiversity. Of 208,000 tonnes of ammonia emitted in the Netherlands in 1993, 181,000 tonnes were estimated to come from manure. [6] According to the Environment Agency, 5% of Britain's Sites of Special Scientific Interest suffer from acidification. [7]