Water is continually moving around, through and above the Earth. It moves as water vapor, liquid water and ice. It is constantly changing its form. The movement of water is referred to as the hydrologic or water cycle. Precipitation, evaporation/transpiration and runoff (surface runoff and subsurface infiltration) are the primary phases in the cycle.

Surface Water

Surface water refers to water that remains on the earth’s surface, in rivers, streams, lakes, reservoirs or oceans.

Groundwater

Groundwater is the portion of water beneath the Earth’s surface that can be collected with wells or which flows naturally to the surface via seepage or springs. California’s enormous groundwater reservoirs are estimated to hold about 20 times the amount of water that is stored behind all the dams in the state. Groundwater doesn’t exist in underground lakes but in the pores and spaces between alluvial materials (sand, gravel, silt or clay) in water-bearing formations called aquifers.

Acre-foot

Water is commonly measured by the acre-foot. One acre foot equals 325,851 gallons. Put ­another way, an acre-foot of water is enough to flood a football field – which is roughly an acre in size – 1 foot deep. The average California household uses between one-half and one acre-foot of water per year for indoor and outdoor each year.