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Groundwater Protection in Selected Countries

3. Water Supply

3.1 The groundwater resource

According to the White Book of Groundwater (Ministerio de Obias Publica, Transportes y Medio Ambiente, 1994), the major aquifers in Spain are approximately equally divided between unconsolidated sedimentary sand aquifers and carbonaceous aquifers. In some limited areas, volcanic rocks must be used for small water supplies. This is the case, for example, on the Canary Islands.

Sand aquifers

There are 4 major basins of unconsolidated sands: Duero, Tajo (Madrid) and Ebro in the central part of the country and Guadalquivir in the south-west. These aquifers are up to 3,000 meters thick. In the largest basin, Duero, measurements indicate a travel time from the recharge area at the edges of the basin to the river discharge at the centre of the basin of 11,000 – 15,000 years. This results in a saline water quality unusable for water supply in the deeper parts of the aquifer close to the discharge. In the Tajo basin, the groundwater is not capable of yielding a sustainable water supply for the large population in the Madrid area. Water table levels have fallen as much as 200 metres in some areas. The extent of the usable aquifers in the Ebro basin in limited due to the presence of low-permeable sediments.

Carbonaceous aquifers

The carbonaceous aquifers are predominantly located in the eastern half of the country and generally contain younger waters. These aquifers are considered very vulnerable.

Dependence on Groundwater

In arid regions, the dependence on groundwater is high, due to the lack of surface water sources. This dependence varies with rainfall. For example, the drought period of 1991-95 resulted in a great dependence on groundwater in the southern part of the country.

3.2 Supply statistics

The main source of water supply in Spain is surface waters. Groundwater supplies between 30 and 35% of the urban supply (Ministerio de Medio Ambiente, 1998). Approximately 2% of the population is supplied with water from desalination.

There are major differences, however, in how much groundwater is used in communities of different sizes. Water supply in communities over 20,000 inhabitants uses only 22 % groundwater while water supply in communities under 20,000 inhabitants uses 70 % groundwater.

The amount of groundwater abstracted in 1994 is estimated at 150 mill. m³ (ITGE, 1999).

Desalination

Desalination is becoming increasingly important in the Mediterranean coastal areas. The desalination process results in the need for discharge of brine wastes. Discharge takes place in some areas by way of injection wells in dolomite rock.

Consumption categories

Consumption of all waters can be divided as follows (Ministerio de Obias Publica, Transportes y Medio Ambiente, 1993):

Figure 3.1.
Total water consumption in Spain by category, 1993.

Consumption of groundwater alone has the following consumption percentages (Ministerio de Obias Publica, Transportes y Medio Ambiente, 1994):

The average water consumption pr. person is approximately 330 litres pr. day (Ministerio de Medio Ambiente, 1998).

Bottled water

A description of drinking water in Spain is not complete without a mention of bottled water (Baeza, 1999). The use of bottled water has developed rapidly in the last 20 years from 394 mill. litres in 1977 to 3,200 mill. litres in 1998. The national average consumption of bottled water is 72 litres pr. person pr. year, but various greatly with the region. In the Canary Islands, for example, bottled water provides approximately 100 % of the water which is ingested.

3.3 Drinking water criteria

Drinking water criteria in Spain are derived from the European Directive 80/778/CEE.

3.4 Cost

The average price charged to the consumer in 1994 was 168 pesetas (White Book, 1998). Of this price, approximately 68 pesetas is used for the actual treatment of the water.

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