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Nature & Environment 2003 – Theme: Water in Denmark

Clean groundwater – an endangered privilege

In Denmark drinking water can be abstracted directly from the groundwater. It is clean, and tastes good. But there is no guarantee that this will always be the case. At some locations, the groundwater has been polluted. The quality of water in the groundwater aquifers is monitored closely, and continuous efforts are being made to protect the aquatic environment in order that clean drinking water can also be provided in the future. The latest initiative was the adoption of the Action Plan for the Aquatic Environment III.

In Denmark almost all drinking water is abstracted from groundwater resources. In the 1990s Denmark used almost 1 billion m³ of drinking water each year, corresponding to the water volume of the ten largest lakes in Denmark. In 2002 consumption of drinking water amounted to approx. 650 million m³. About one-third is consumed by private households, one-third by agriculture and horticulture, and one-third by industry and institutions. In the last decade the consumption of water has fallen by 40 per cent. In densely populated urban areas, for instance the cities of Copenhagen, Århus, and Odense, the water abstracted exceeds the volumes recharged to the groundwater aquifers. Therefore the watercourses are drying out in the summer, and the groundwater table is decreasing.

From groundwater to drinking water

Raw groundwater can be used directly for drinking water purposes at only very few locations. Before drinking water is supplied to consumers, it is aerated and filtered in order to remove most of the naturally occurring iron, manganese, and methane. Most often, aeration and filtration is sufficient treatment.

Danes live on top of the water they drink. Waterworks are located throughout Denmark. This decentralised structure presents a lot of advantages: it contributes to good groundwater and drinking water quality in large parts of the country, and it allows consumers to keep an eye on the quality and to identify possible solutions to pollution threats.

Most of the 3,000 large waterworks operate with borings that reach the groundwater 20-200 metres below the surface. In addition, approx. 70,000 private wells or borings, each supplying less than 10 households, abstract water from layers of sand, gravel, and limestone close to the surface.

Denmark wants clean groundwater – not treated groundwater

Denmark wants to produce drinking water from unpolluted groundwater. This was the attitude of previous governments – and it still applies. However, waterworks find it increasingly difficult to abstract high-quality raw water from the subsoil. The major contributors to groundwater pollution are nitrate, pesticides, and organic solvents. Nitrate and pesticides come from cultivated fields, gardens, green and built-up urban areas, golf courses, and roadsides. Organic solvents come from old waste dumps, dry cleaning establishments, and industrial sites.

Over the last 15 years, more than 700 waterworks have closed down because the quality of the raw water had become unacceptable.

Danish water policy is based on prevention and implementing measures at source. Of course cleaning is just one of a broad range of options available when identifying solutions to a specific pollution problem. But it should not be the first choice of the waterworks when faced with polluted borings. In cases where it is neither technically nor economically feasible to replace the polluted groundwater by clean groundwater, treatment can be a solution to the specific pollution problem.

Over the last decade, water consumption has fallen by 40 per cent, in part because of green taxes. The figure shows total water abstraction and consumption broken down by common waterworks, commercial irrigation, and industry

Source: Geological Survey of Denmark and Greenland

The indicator shows the volumes of groundwater abstracted in Denmark since 1989, broken down by three main types: common waterworks (i.e. waterworks supplying at least 10 properties), commercial irrigation, and industry.

Over the last decade, the total consumption of groundwater has fallen by almost 40 per cent. In 2002 the total volume of groundwater abstracted was 653 million m³, or somewhat less than in 2001. The pale green section of the column indicates that, of the total volumes abstracted, 410 million m³

was used for drinking water purposes, thus continuing the almost constant fall in private consumption since 1989. 98 per cent of drinking water is abstracted from groundwater aquifers, and the remaining 2 per cent from surface water. The fall is partly due to green taxes on the price of water – an efficient water-saving incentive.

With the implementation of the EU Water Framework Directive, a number of new environmental targets for groundwater must be introduced in Danish law. When setting the targets, the entire hydrological cycle, i.e. the impact of groundwater on other parts of the hydrological cycle, is considered. For instance the magnitude of the impact on surface water in watercourses and lakes should not prevent compliance with the environmental targets set for groundwater.

The figure illustrates the exploitable groundwater resources and how they are used. In densely populated areas and in areas of light soil requiring extensive irrigation, the water is used more quickly than the aquifer recharge rate.

Source: Geological Survey of Denmark and Greenland

A new survey of the groundwater available for drinking water purposes estimates 1.0 billion m³

water is available per year. In earlier calculations this figure was 1.8 billion m³ per year. However, this does not indicate that the volumes available for drinking water, for instance, are smaller than before. What it does indicate is that it is now possible to include the entire freshwater cycle in the calculations.

Thus, the survey assumes a maximum allowable magnitude of impacts on watercourses in relation to the existing objectives. This assumption forms the basis of the calculation of the maximum groundwater abstraction.

Around large cities, the volumes of water abstracted today exceed the exploitable groundwater resources. In Northern Sealand and around Copenhagen, the groundwater resources are being over-exploited by almost 80 million m³/year; on Funen by almost 10 million m³/year and; in Eastern Jutland by approx. 30 million m³/year. At some locations in the Copenhagen area, more than three times the exploitable resources are being pumped up. These figures result from the fact that the calculation is based on environmental targets that do not fully reflect the simple fact of nature that, when large volumes of water are abstracted, the water volumes available to safeguard recreational and natural interests are reduced.

Moreover, some of the upper groundwater aquifers are so contaminated that they cannot be used for a number of years. Pollution of the upper groundwater levels increases the need to base water supply on deeper groundwater. Therefore, in the densely populated areas around Copenhagen, Odense, and Århus, and on light soils in Central and Western Jutland where field irrigation is required, the volumes of water abstracted exceed the water recharged to the aquifers.

Water abstraction, and abstraction for irrigation in agriculture in particular, depends largely on the climate, and therefore the volumes pumped up vary greatly from one year to the next. In 2002 abstraction for irrigation was modest, and in the areas in Southern Jutland and in Ribe and Ringkjøbing counties, where the need for field irrigation is considerable, the degree of exploitation was well below 100 per cent. In dry seasons, when the need for field irrigation is large, for instance in 2003, the degree of exploitation increases considerably, to about three times as much.

The overall quantities of pesticides sold in Denmark fell significantly in the period 1981-2002. The green columns show that sales decreased by one-third. The annual quantities of pesticides sold to agriculture – the blue columns – more than halved.

Source: The Danish EPA

The indicator shows the trend in sales of pesticides in the period 1981-2002. The green columns represent the total quantity of all types of pesticides (plant protection products and biocides, including wood preservatives) sold in the period. The blue columns are agriculture's share of the pesticides sold.

From 1984, when sales peaked, to 2002, annual sales of pesticides to agriculture fell from 6863 tonnes to 2868 tonnes, a 58 per cent decrease.

In this period application frequencies fell from 3.2 to 2.04, or by 33 per cent. Application frequencies indicate how many times per year the pesticides sold can be applied to agricultural land, when used in standard doses. Application frequencies thus reflect the application intensity by agriculture, and are indicators of the impact on the environment. Calculations show that the consumption of pesticides fell more than the application frequency. The reason is that the pesticides used today are effective in much smaller doses, thus reducing consumption, but not necessarily the impact on the environment.

Part of the explanation for the general decrease in sales of pesticides is the voluntary agreement between the local, regional, and state authorities, to introduce pesticide-free weed control in public areas. Since 1995 consumption at local level has fallen by 74 per cent, at regional level by 79 per cent, and at state level by 42 per cent.

The Government's Pesticide Plan 2004-2009 sets the goal of reducing application frequencies to 1.7. The Plan also focuses on horticulture and fruit growing, and cultivation guidelines and catalogues of methods to reduce the use of pesticides are being prepared. The objectives of the Plan also include the use of pesticides in private gardens.

Pesticides or their metabolites are found in one out of three abstraction wells analysed. The indicator shows findings of pesticides in abstraction wells.