Groundwater, which is found in aquifers below the surface of the earth, is one of the nation's most important natural resources. Groundwater provides drinking water for a large portion of the nation's population, supplies business and industries, and is used extensively for irrigation.
Groundwater can also contribute to surface water supplies. Some groundwater seeps into rivers and lakes, and can flow to the surface as springs.
The water level in an aquifer that supplies water to a well does not always remain the same. Droughts, seasonal variations in precipitation, and pumping affect the height of underground water levels. If a water is pumped at a faster rate than an aquifer is recharged by precipitation or other sources of recharge, water levels can drop. This can happen during drought, due to the extreme deficit of rain.
Long-term water-level data are fundamental to the resolution of many of the most complex problems dealing with groundwater availability and sustainability. Significant periods of time - years to decades - typically are required to collect water-level data needed to assess the effects of climate variability, to monitor the effects of regional aquifer development, or to obtain data sufficient for analysis of water-level trends.