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 |
Principle aquifers
The principle aquifers in England belong to the geological sequence called the Younger Cover (from the Permian and the Quaternary sequence) and are found in the Lowlands of England (southeast). The most important aquifers are found in:
 | Cretaceous chalk |
| Permo-Triassic sandstones |
| the Jurassic limestones |
| Lower Greensand from the Cretaceous period. |
It should be mentioned, that the specific yield of these aquifers varies greatly from about 1% in chalk to 20-25% in sandstones, meaning that more than 20 times as much water can be stored in the sandstones.
Replenishment
The average annual replenishment to the main aquifers of the Younger Cover is 7 billion m3 (UK Groundwater Forum, 1998). The total groundwater abstraction in England and Wales in 1995 was 2.4 billion m3 (Water Services Association, 1998), or about one-third of the exploitable resource. Figure 3.1 shows an overview of replenishment and abstraction for the principle aquifers.
figure 3.1
Comparison of replenishment and abstraction of groundwater for the principle
aquifers of the UK (UK Groundwater Forum, 1998).
Artificial recharge
Artificial recharge of the groundwater is used in the London area where surplus surface water from the river Thames and Lee is treated and recharged into the Chalk. In dry summers, the stored water is pumped from the aquifers, treated once again and then distributed. The use of artificial recharge is expected to be increasingly used in the future. Climate changes in connection with the greenhouse effect may also cause even greater seasonal changes (drier summers, wetter winters), making this scheme even more valuable.
Groundwater stored in the Triassic sandstones aquifer in Shropshire is used to regulate the flow of the River Severn and thereby supply water for many communities.
Groundwater age
The age of groundwater in England varies from aquifer to aquifer but a significant proportion is quite old. For example, groundwater in the Chalk in the centre of the London Basin contains a component that is some 20,000 years old.
3.2 Supply statisticsGroundwater provides about one-third of public water supplies in England. There are, however, large geographical variations. In the southeast, over 70% of the public supply stems from groundwater, while in the north, use of surface water prevails. In Scotland, for example, only 3% stems from groundwater. This is largely due to the location of the primary aquifers mentioned above.
The public water supply accounts for the greatest consumption of groundwater, while industry, fish farming, mineral washing and spray irrigation also use significant amounts. Figure 3.2 is a graphic representation of these categories.
Figure 3.2.
Water consumption in England by category, 1995 (Water Services Association, 1998).
In 1997, domestic consumption was 160 l pr. person pr. 24 hours. In 1961, the domestic consumption was 85 l pr. person pr. 24 hours.
3.3 Water supply structureIn England and Wales, there are approximately 2,000 public groundwater supply sources. These are operated by private companies. There are no policies to centralise or to decentralise these sources. However, the pattern of public supply is generally based on large abstractions supplying communities through relatively long distribution networks.
3.4 Water treatmentTypical treatment
Typical treatment of groundwater is a precautionary chlorination followed by dechlorination, both at the source. There is some filtration of sources with high natural iron or manganese content. There is little use of activated carbon.
Advanced treatment
About 30 sources have been affected by industrial contamination and have either been abandoned or treated by air stripping or carbon filtration. Elevated levels of nitrate are generally dealt with by blending whereas ion exchange is used at a very few sources.
3.5 Drinking water criteriaThe Drinking Water Regulations include criteria for drinking water and reflect the European Drinking Water Directive. The actual criteria are included in the appendix1.
3.6 CostThe annual water charge in London is approximately 125 ECU (Water Services Association, 1998). This charge is for a use of approximately 200 m3, meaning that the price pr. cubic metre is about 0,62 ECU.