Groundwater Protection in Selected Countries
3. Water Supply
| 3.1 | The groundwater resource |
| 3.2 | Supply statistics |
| 3.3 | Water supply structure |
| 3.4 | Water treatment |
| 3.5 | Drinking water criteria |
| 3.6 | Cost |
The Water Board estimated in 1992 that the viable exploitable groundwater in Denmark is 1,800 mill. m3 pr. year (Miljøstyrelsen, 1992). This estimation was based on net precipitation, and experience in the exploitable percent of this precipitation in various groundwater aquifers types. Reductions in the exploitable groundwater due to extended climate variations and groundwater pollution were not included in this number. It has been estimated that between approximately 20 and 80 mm/year are exploitable in different regions of the country.
Resources model
A mathematical model based on the commercially available software MIKE SHE is currently being prepared by the Geological Survey of Denmark and Greenland (Vandmodel, 1999). This National Water Resources Model has the purpose of determining the size of the exploitable groundwater resource and is intended to be appropriate for analysing effects of time-dependent climate variability, groundwater-surface water interaction, regional distribution and future water consumption scenarios. The first estimates are expected in the year 2000.
Major aquifer types
Groundwater in Denmark is abstracted from a variety of aquifer types. The most important are:
 | aquifers in Quaternary glacial melt water deposits, consisting of sand and gravel |
| aquifers in Tertiary marine and fresh water deposits, consisting of sand and gravel |
| aquifers in Tertiary and Cretaceous marine deposits, consisting of fractured limestone. |
The vulnerability of these aquifers depends on the nature of the cover layers. These cover layers can often be glacial deposits, consisting of clayey tills. In some fewer cases the cover layers can consist of buried Tertiary clay deposits.
The age of groundwater in Denmark varies from aquifer to aquifer but is generally thought to be quite young. Estimates suggest that nearly half of the groundwater used for water supply is less than 50 years old.
3.2 Supply statistics
Water supply in Denmark is based almost entirely upon groundwater. Although surface water is utilised in a limited number of cases for industrial purposes, only two waterworks, Sjælsø and Regnemark utilise surface water for drinking water purposes. Thus, 99.6% of the water abstracted by the common utilities in Denmark in 1997 came from groundwater.
The amount of water abstracted by the common water supplies in 1997 was 457 mill. m3. Although only 6% of the common utilities are public, they accounted for 64% of the water abstraction. Household use comprises 60,4% of consumption and is by far the largest consumption category. Household use is followed by industrial use (22.6%), institutions (8.5%) and water loss (8.6%).
The amount of water abstracted for irrigation purpose in 1997 was 369 mill. m3 and is therefore nearly as large as the other consumption categories put together. Included in this amount is irrigation for agriculture/nurseries, fisheries, athletic fields and parks (GEUS 1998). The amount of irrigation varies considerably from year to year, primarily due to varying need for irrigation.
Figure 3.1 is a graphic representation of these categories.
Figure 3.1.
Water consumption in Denmark by category, 1997.
In 1997, household consumption was 136 litres pr. person pr. 24 hours, a reduction of 21% over the past 10-year period. In the same time period, industrial use has fallen 12% and institutional use has fallen 21%.
Water loss has also fallen the past years from approximately 10.6% go 8.9%. The specific water loss has fallen from 5.2 to 2.7 m3 pr. kilometre pipeline pr. 24 hours. Due to variations in the which water supplies have reported, these numbers are not exact.
The specific energy consumption for the production of drinking water has been nearly constant over the past years at 0.40 kWh pr. m3.
3.3 Water supply structure
The water supply structure in Denmark exhibits a high degree of decentralisation. In 1997, there was a total of 2,919 common utilities, composed of 2,743 private and 176 public suppliers. The number of suppliers has dropped 13% over the last 10 years and 25 % over the last 17 years. According to a recent report (Miljøstyrelsen, 1997a), the number of suppliers is expected to continue to decline in the coming years, largely due to increasing finds of pesticide contamination.
It should be noted that the highly decentralised structure is somewhat deceptive since there are a few large suppliers and a great many small suppliers.
In addition to the common utilities, it was estimated that an additional 93,000 private wells and small utilities were in existence in 1995.
In 1997, the Drinking Water Committee initiated an analysis of the water supply structure in Denmark with the purpose of determining if the current regulations afford an adequate protection of the groundwater. A prerequisite for this analysis set forth by the Committee was that the current decentral structure be maintained as much as possible.
The analysis concluded that it is possible to maintain the decentralised structure. However, over the next 10 years an estimated 345 common utilities will be forced to close and 10% of the remaining will require advanced water treatment (Miljøstyrelsen, 1997)
3.4 Water treatment
The great majority of water supplies in Denmark treat their raw water using only aeration and filtration. In a number of supplies, calcium carbonate is added. Only a handful of supplies use other processes. These include disinfection with UV- irradiation, methane removal by stripping and adsorption with granular active carbon.
3.5 Drinking water criteria
Two types of criteria are used in Denmark. Firstly, guidelines for the quality of raw water used for production of drinking water are given for a large number of parameters (Miljøstyrelsen, 1998a).
In addition, quality criteria for drinking water are given in the regulations (Miljøministeriet, 1988). Both of these criteria are given in Appendix 2.
3.6 Cost
The average price charged to the consumer in 1997 was 26.0 DKK pr. m3. Of this total, 5.1 DKK went to the suppliers and 4.0 DKK to a special water tax. The remainder was shared by sewage treatment plants (11.6 DKK) and state (5.2DKK). The total price charged in 1997 ranged from 13 DKK pr. m3 to 45 DKK pr. m3, a factor greater than 3.
Using the sum of the price to the suppliers and to the special water tax (9.1 DKK), and assuming a total abstraction of 457 mill. m3, a total of 4,159 mill. DKK was used for water supply in 1997.