Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

What Is This Indicator, and Why Is It Important? This indicator would report the percentage of the area of the nation’s major regional aquifers in which water levels are increasing, decreasing, or stable. The indicator would report what fraction of the aquifer area declined, increased, or remained stable in comparison to a previous period, and it would be reported every 5 years.

Groundwater provides about 40% of the nation’s municipal water supply and is the source of much of the water used for irrigation. For most people in rural America, groundwater from their own wells is their only source of water. Groundwater is a major contributor to flow in many streams and rivers, and it has a strong influence on river and wetland habitats for plants and animals.

Why Can't This Indicator Be Reported at This Time? Data on groundwater levels are collected by federal, regional, state, and local agencies. All states have some coverage, but there are areas of the country for which very little information is available. The data that do exist have not been aggregated to provide systematic measurements of water levels in a significant portion of the nation’s major aquifers.

The first step in producing national coverage would be to locate and assess the quality and consistency of existing data. It would then be necessary to aggregate those data and determine where there is sufficient geographic coverage of the major aquifers and adequate characterization of conditions in those aquifers. In areas where data coverage is inadequate, additional measurements would be necessary.

Discussion Changes in water levels reflect changes in the amount of groundwater pumped from or returned to major aquifers; changes may also reflect climate variability or climate change. The measure reports on changes in the quantity of groundwater: it does not address the quality of that water or its suitability for use.