Summary Sustainable use of groundwater to meet long-term drinking water and agricultural needs. General Information What is it? Changes in the depth to groundwater is a straightforward way to track both depletion and replenishment of underground aquifers. Water scientists and managers monitor the depth and change in depth to groundwater in wells throughout California. If the rate of depletion or use of groundwater is greater than the rate of replenishment, then there will be a net decline in depth to groundwater from year to year. If the rate of depletion is matched by the rate of replenishment, then there will be no net change in depth to groundwater. In some cases, for example in aquifers recovering from over-use, there may be a net gain in groundwater, meaning the depth to groundwater will get shallower over time. Why is it important? Groundwater provides a consistent source of water for drinking and irrigated agriculture during droughts and dry seasons. In some very dry areas it may be the primary source of water and may get depleted over time due to over-use. Most of the agricultural areas in the Central Valley depend on groundwater to provide most irrigation water during some or most of the year. Many community drinking water systems also depend on groundwater wells to meet part or most of their water needs. What can Influence or Stress Condition? When groundwater is used at a greater rate than it can be replenished, then depth to groundwater will increase. This can happen when there are too many users, and/or if there is an extended drought. If groundwater is recharged naturally or artificially at a greater rate than it is depleted, then the depth to groundwater will decrease. Target or Desired Condition The desired condition is that depth to groundwater does not increase statistically over time. If use is sustainable and aquifers are being replenished, then their should be no net change in depth over several years of monitoring. The undesired condition is that there is a statistically-significant net increase in depth to groundwater over time.
