Local Water Utilities United for Safe Drinking Water

Residence Time of Groundwater

The length of time water spends in the groundwater portion of the hydrologic cycle may be as little as days, or as much as 10,000 years or more. This is called “residence time.” For example: A raindrop may fall to the earth’s surface. It may seep down through the soil to a saturated zone or aquifer only to pumped back to the surface and sprayed from a garden hose and back down again.

Estimated depth and residence time of the world's water supply

WaterEquivalent depth (meters)Residence Time
Oceans/Seas2500~4000 years
Lakes/Reservoirs
.25~10 years
Swamps.007~1-10 years
Rivers.003~2 weeks
Soil Moisture.13~2 weeks-1 year
Groundwater120~2 weeks-10,000 years
Ice caps/Glaciers6010-1000 years
Atmospheric water.025~10 days
Biospheric water.001~1 week

How Much Water Exists?

The Earth is 70% Water. Less than 1% is groundwater. In fact, over 99% of all water is not available for our use. So where is all the water? The Earth’s water is all around you. Water is in streams, lakes, oceans and rivers. This water is called “surface water.” But … there is more to our water supply than surface water. There is plenty of water beneath our feet, in the ground as soil moisture and in aquifers.

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