Groundwater Protection in Selected Countries
3. Water Supply
| 3.1 | The groundwater resource |
| 3.2 | Supply statistics |
| 3.3 | Drinking water criteria |
| 3.4 | Cost |
Aquifer regions
On the basis of geological settings, a subdivision of the United States in 4 major aquifer regions can be made:
- The western mountainous region (including Alaska and Hawaii)
- The Midwest plains
- The eastern mountainous region
- The coastal plains of the Atlantic and the Gulf of Mexico.
The character of the aquifers in these regions is highly variable and relates closely to the regional geological formations. The aquifers range from low-yielding bedrock such as granite and shale, to high-yielding sand, gravel and limestone. The most widespread aquifers of the United States are found in the Midwest region between the mountain ranges to both the east and the west. Sediments from the mountains have been transported to the lower lying plains for a long period of geologic time.
A general overview of the aquifers of the 4 regions is given below (USGS, 1998):
- The western mountainous region
In this region, the unconsolidated aquifers of the mountain ranges dominate. In Alaska and other large areas, however, only low-yielding bedrock aquifers can be found. In the northwest and Hawaii, basaltic and volcanic aquifers are found.
- The Midwest plains
In this region, sandstones of the Colorado Plateau and unconsolidated sands of the High Plains dominate. In large areas, only low-yielding bedrock aquifers can be found.
- The eastern mountainous region
Carbonate and sandstone aquifers of the mountain ranges can be found in this region, but very large areas have only low-yielding aquifers.
- The coastal plains of the Atlantic and the Gulf of Mexico.
Unconsolidated sands of the Mississippi Valley and surrounding areas and semiconsolidated sandstones of the coastal plains dominate. Only a small percentage of the area has low-yielding aquifers. In the south-eastern most part of the region the aquifers are primarily surficial.
The vulnerability of the aquifers depends on the nature of the cover layers and because of the geological variability a general overview can not be made.
3.2 Supply statisticsGroundwater supplies the overall population of the USA with 51% of its drinking water. In rural area, groundwater supplies 95% of the population with drinking water (data from 1990).
Approximately 63% of the groundwater use in the USA is for irrigation purposes. Water supply represents 19% of groundwater use while industry represents only 5%. Figure 3.1 shows the groundwater consumption in the USA by category.
Figure 3.1.
Water consumption in the USA by category.
There are two main categories of drinking water standards: primary and secondary.
MCLs
Primary standards are enforceable standards that apply to public water systems. They limit the levels of specific contaminants that can adversely affect public health and are known or anticipated to occur in water. The primary standards are called maximum contaminant levels or MCLs.
Secondary standards
Secondary standards are non-enforceable guidelines. They refer to levels of contaminants that may cause cosmetic or aesthetic effects. The individual states may choose to adopt these standards as enforceable.
MCLGs
A third standard is the maximum contaminant level goal. This is a non-enforceable public health goal at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety. MCLGs are based only on health risks and may exceed current capabilities of treatment technology and analytical detection limits.
Appendix 1 is a list of MCLs.
3.4 CostThe 1997 National Utility Service International Water Price Survey examined water costs for public water supplies based on 51 cities throughout the united States (Water Well Journal, 1998). In this survey, costs were found to range from 0.20 USD pr. m3 to about 1.00 USD pr. m3. The survey showed that water prices in the USA are among the lowest of the countries surveyed, with Germany being the most expensive and Norway the least expensive.