What is Groundwater

There are two types of water below the surface:
- Soil moisture, in the unsaturated zone that contains both air and films of water in the spaces between soil particles. This is the water used by plant roots.
- Groundwater is subsurface water that completely fills (saturates) the pore spaces of soil or rock formations below the water table, which is the upper surface of the saturated zone.
The saturated zone can be made up of many different layers of soil or rock formations.
Groundwater is in constant motion. Like surface water, groundwater flows downhill by the force of gravity. Groundwater also flows from areas of higher pressure to areas of lower pressure.

Groundwater flows along smooth flow paths except in fractured rocks and limestone type aquifers.

Groundwater flows at different rates through different soil types. For example, sandy soils contain larger pore spaces (they have higher permeability) than clay soils, but do not contain as much total pore space as clay soils.

Because of this, groundwater moves more quickly through sandy soils. Clay soils have a higher porosity, and tend to hold water (like a sponge). Groundwater moves much more slowly through clay soils.

Institute of Water Research - MSU
Design by Alex Morese