The zone of saturation is the portion of underground soil where all gaps are completely filled with water.

In general, all of the soil and rock that is underground is divided into the zone of aeration and the zone of saturation. The main difference between these two large zones has to do with what is located in between the pores (gaps) of soil or rock particles.

Water that seeps into the ground is called ground water. First it enters the zone of aeration, which is closer to the surface. The pores in the zone of aeration are filled with either air or water. Plants rely on this ground water for nourishment as they absorb it with their roots.

The ground water keeps moving down, however. If we dig deep enough, all of the space in between rock and soil particles will be filled with water. That’s the zone of saturation. The zone of saturation happens naturally as water (from rain and other sources) is pulled deep underground by gravity.

The location where the zone of aeration and zone of saturation meet is called the water table. All of the ground underneath the water table is located in the zone of saturation.

The term zone of saturation has been used since at least the 1890s. Since that time, it has been used in geological surveys and reports interested in the study of ground water.

Because the zone of saturation is defined by the complete saturation of water, its location can range from several feet to several hundred feet below the surface, depending on the environment. Beaches and coasts, for example, will have zones of saturation that are very close to the surface.

The water table can also be higher or lower, depending on where the top of the zone of saturation is. The water table can rise or fall due to natural events such as heavy rain, droughts, and flooding. Human activity can also affect the zone of saturation and the water table. Most drinking water comes from underground reservoirs or aquifers. If water is pumped out faster than it can naturally saturate the ground, the water table will fall. If it gets really low, the zone of saturation sinks lower than the well can reach and no water can be pumped out.

If the top of the zone of saturation (the water table) reaches the surface, it creates a unique type of environment known as wetlands. Wetlands are home to many kinds of plants of animals that rely on the large amounts of water in the soil. Wetlands provide a lot of benefits to the ecosystem, so conservation organizations are highly concerned with protecting them.

This diagram shows a basic representation of the major zones located underground. You can see that the ground located in the zone of saturation is entirely soaked with water.

Friday fact: The water table is the top of the zone of saturation and the level below which soil and rock are saturated with water. #groundwater #watertable pic.twitter.com/KGjCSe7y8i

— The Groundwater Foundation (@groundwaterfdn) April 10, 2020

Students are often introduced to the zone of saturation when learning about ground water and the water table.

6th hour discussion on rain and drought to the water table and zone of saturation. Great job. pic.twitter.com/NfAsrwZSDe

— Rebecca Greenway (@greenwaysclass) June 7, 2016

Zone of saturation: The subsurface area where water fills the openings of the rock.
Water table: The upper part of the zone of saturation.
Zone of aeration: The area between the water table and ground surface.
A bountiful water well is drilled into the zone of saturation. pic.twitter.com/msA34ossCx

— HGGRC (@HGGRC_Hawaii) October 13, 2018

• water table
• soil
• ground water
• saturation
• aquifer
• drinking water
• well
• phreatic zone

True or False?

In the zone of saturation, the pores between the soil and rock are completely filled with water.