|Oroville Dam, California|
California gets it water from three sources, about a third each from: precipitation, snowpack, and aquifers (groundwater). In many areas of the state, groundwater systems have been depleted for long periods - even between droughts - from which they have not recovered.
Excessive, long-term groundwater over-use resulting in groundwater depletion can cause subsidence and permanent loss of groundwater storage as well as water quality degradation and seawater intrusion. These long-term impacts on groundwater have not been remedied by the recent weather. If recovery is possible, it will likely take several to many years to accomplish.