# What is Groundwater? - Definition & Explanation

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• 0:02 What Is Groundwater?
• 0:52 Porosity & Permeability
• 2:06 Aquifer
• 2:33 Issues with Groundwater
• 3:31 Lesson Summary

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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

Groundwater accounts for up to 20% of all the fresh water on Earth. This lesson will explain what ground water is and its important aspects. Once you've finished the lesson, test your understanding with a quiz.

## What Is Groundwater?

The simplest definition of groundwater is that it is water that is underground. Of all the fresh water on Earth, about 20% is groundwater. As water seeps into the ground, it continues downward due to gravity until the surrounding ground is saturated with water.

As it moves, water takes up the available spaces between particles underground and moves in the direction of least pressure. When you have groundwater, you have a water table, which is the line where saturated and unsaturated layers meet. If you know how a well works, you may know about water tables because in order for a well to be able to pump water, it must be as deep as the water table.

Now, let's talk about some other factors related to groundwater.

## Porosity and Permeability

The ability for the ground to hold water depends on two main factors, porosity and permeability.

Porosity is the amount of free space within a material. In the case of groundwater, that material is the ground. Imagine pouring water onto sand at the beach. It will sink right in and that's because sand has high porosity. Lots of free space inside it to hold the water. On the other hand, if you pour water onto a sidewalk, it will stay there until it evaporates away. That's because cement has very low porosity. It's very tightly packed together and can't hold water.

The other factor is permeability. Permeability is how connected the free spaces in a material are. This helps determine if the water can move or transfer through the ground or other material. For example, a cloth is highly permeable; the free spaces are tightly connected and so water is able to pass through the cloth via the network of connected free spaces. On the other hand, a plastic bag is not permeable. The free spaces are not well connected, and so water cannot pass through the plastic.

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