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Chartered Institution of Water and
Environmental Management (CIWEM)

106-109 Saffron Hill, London, EC1N 8QS  
Tel: 020 7831 3110   Fax: 020 7405 4967

Diffuse Pollution of Water


The Chartered Institution of Water and Environmental Management (CIWEM) is the leading professional and qualifying body for those responsible for the stewardship of environmental assets. The Institution also provides independent comment on water and environmental management and sustainable development. This paper sets out recommendations for tackling diffuse pollution.

Diffuse pollution originates from hundreds or thousands of small sources, or is washed off land with rainfall. It is distinct from point sources like discharges of wastewater from industrial treatment plants, and it is more difficult to control.

Diffuse pollution is now more evident since the quality of point source discharges has been improved. Diffuse pollution can affect water supplies, effluent disposal, industry, fisheries, recreation, and conservation. Most diffuse pollutants stem from the use of land for agriculture, forestry, industry and from urban land.

CIWEM is pleased that the Department for Environment, Food and Rural Affairs (defra) has set out its priorities for policy in Directing the Flow . This recognises the significance of diffuse pollution.

CIWEM's Position on Diffuse Pollution of Water

  1. CIWEM seeks cost effective policy measures for addressing diffuse pollution, developed in consultation with stakeholders. CIWEM supports approaches that emphasize outcomes and achieve specific reductions of risks.
  2. CIWEM supports the promise in Directing the Flow to review, and to consult more widely on problems caused by agricultural activity.
  3. CIWEM supports the way in which the forestry, agriculture and construction industries have adopted "codes of good practice". These should be written into binding Codes of Practice under the Water Framework Directive.
  4. CIWEM suggests that a statutory Code of Practice should be developed along the lines of the present Environment Agency's 'Best Farming Practices' and the Scottish Agricultural Pollution Group's PEPFAA (Prevention of Environmental Pollution from Agricultural Activity) codes. This would address risks to drinking water, bathing water and from eutrophication.
  5. CIWEM suggests stronger incentives to prevent pollution. These can include, cost-savings, the avoidance of fines and tax advantages.
  6. CIWEM seeks to ensure that land use planning guidance and good practice at both national and regional level takes more account of water.
  7. CIWEM advises that more emphasis be placed on the risks to private water supplies.
  8. CIWEM wants more research, and more collaborative research, on:
    • urban diffuse pollution, and policy options to address it;
    • implications of land-use planning decisions;
    • scope for sustainable drainage systems (e.g. SuDS) to help to prevent pollution; and,
    • the cost-effectiveness of options to alleviate and prevent diffuse pollution.
  9. CIWEM seeks more weight for the biodiversity implications of options for addressing diffuse pollution, and the promotion of sustainable farming practices.
  10. In determining action, CIWEM believes that because of the multitude of stakeholders involved that all the costs and benefits need to be taken into account. The involvement of different groups should also be identified clearly. Those responsible for pollution should pay most of the costs. This should lead to more effort to control discharges to and from surface water sewers, and to reduce chemicals entering the environment.
  11. CIWEM suggests that EC Directives take more account of costs and benefits before they are agreed and before being transposed to UK law a Regulatory Impact Assessment (RIA) is undertaken. A wider range of stakeholders should be involved in the consideration of proposals for Directives.
  12. Such a cost benefit appraisal should consider the principles of sustainability, the environmental, social and economic costs, and the search for solutions that give most overall value and benefit to society.
  13. In promoting a more sustainable agriculture CIWEM supports reforms of the Common Agricultural Policy to take account of environmental directives, including water, and encourage improvements to environmental performance.

1 Directing the Flow - Priorities for future water policy, published by Defra in November 2002

Background information: sources and impacts of diffuse pollution

Industrial activities may generate diffuse pollution by oils and hydrocarbons, sediment, phosphorus, iron, acidifying pollutants through atmospheric emissions, and chemicals such as solvents. On industrial estates, activities are carried out on yards drained by surface water sewers. These can discharge direct to rivers.

Pollutants are washed off impervious surfaces and can arise through (illegal) mis-connections to sewers. These can cause pollution by oils, hydrocarbons, pesticides, organic wastes, faecal pathogens, nutrients, chemicals from detergents, and products used in gardening. The use of pharmaceuticals and cosmetics has increased the load of substances like zinc.

The use of sustainable drainage systems (often known as sustainable urban drainage systems, or SuDS), which can contain and partially treat runoff naturally, can help to mitigate the pollution from runoff if well designed.

In agriculture, livestock numbers have increased, with corresponding risks of soil erosion and contamination associated with organic wastes. Recent changes in crops, with a push for higher productivity, have been associated with more use of fertilizers, and a reliance on pesticides to control weeds and disease. Most incidents of diffuse pollution of drinking water supplies have been attributable to agricultural sources.

Nitrate has a potential impact on health and standards have been imposed for drinking water. The origin of 70 per cent of this nitrogen is associated with agriculture. A threat to drinking water standards for surface and groundwaters has lead to the designation of Nitrate Vulnerable Zones for land draining to waters that are non-compliant. In these zones farmers must comply with limits on nitrate applied to land (the requirement to reduce nitrate concentrations for drinking water incurs costs for the treatment or blending of water supplies).

Nitrogen in coastal waters is also said to be the key risk factor for eutrophication. Where waters are identified as "polluted" because they show signs of eutrophication, the contributory catchment(s) must be designated as a Nitrate Vulnerable Zone.

The use of organic wastes in agriculture has also raised concerns. The main diffuse source of faecal pathogens is from livestock, although locally significant sources include urban land, recreation areas and domestic buildings (for example, wrong connections, and bird roosts on roofs and lakes). These can threaten standards for bathing waters, despite the recent big improvements to sewerage systems. Apart from the real and perceived risk to public health, this causes a loss of income from tourism because of bad publicity. In addition, monitoring is expensive with systems costing around £100,000.

There are risks from livestock of Cryptosporidium in public water supplies. Barriers forCryptosporidium cost £10 million for a large water treatment works.

Recreational activities such as golf, sports field management, boating, camping and pet exercising contribute to risks from oils and hydrocarbons, pesticides, suspended solids, faecal pathogens or nutrients.

Organic solvents and pesticides are amongst the most frequently occurring contaminants of groundwaters. The annual cost to the water industry in the UK for treating pesticide contamination of drinking water is significant.

Litter, oil films, anoxic sediments, and algal blooms can have an impact on the quality of lakes and streams, and be a nuisance to recreation. The risks of toxic algal blooms and potential exposure to faecal pathogens impose costs in providing drinking water.

Diffuse sources of phosphorus from land surfaces come from a range of sectors. The water industry provides a substantial input from point sources. In areas designated as sensitive to eutrophication because of phosphorus under the Urban Wastewater Treatment Directive, phosphorus removal is required at large sewage treatment works.

The main impacts for the water industry of eutrophication are increased treatment costs as a result of algal blooms. These can, in some cases, also deplete dissolved oxygen and affect fisheries and are dangerous to livestock and domestic animals. Phosphate can also affect plants, displacing sensitive species of high conservation value.

Phosphorus is also considered to be a threat to lakes. Waterfowl depend on good water quality for the aquatic plants and invertebrates on which they feed.

Many costs of diffuse pollution are not borne by the polluter. Government, industry and households pay. Impacts on agricultural or fisheries may increase the price of our food.

May 2003

Note: - CIWEM Policy Position Statements (PPS) represents the Institution's views on issues at a particular point in time. It is accepted that situations change as research provides new evidence. It should be understood, therefore, that CIWEM PPS's are under constant review, that previously held views may alter and lead to revised PPS's


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Chartered Institution of Water and
Environmental Management (CIWEM)

106-109 Saffron Hill, London, EC1N 8QS  
Tel: 020 7831 3110   Fax: 020 7405 4967