Groundwater

Groundwater is the water found deep under the Earth in spaces between rocks and soil. It makes up about 30 percent of all the fresh water we can easily use. When rock or soil can give us useful amounts of this water, we call it an aquifer. The level where water fully fills these spaces is known as the water table.

We get groundwater from rain and other water that soaks into the ground. It can come out naturally in places called springs or seeps, and it helps create oases and wetlands. People also dig wells to reach groundwater for drinking, farming, and many other uses. Studying how groundwater moves is called hydrogeology.

Groundwater is important because it is often cleaner and easier to use than water on the surface. Many communities rely on it for drinking water, and it stores more water than all the lakes and reservoirs together in places like the United States. However, using groundwater can cause problems, like pollution from waste and chemicals, and sometimes the land can sink when too much water is taken out. These issues are made harder by changes in the climate and rising sea levels.

Definition

Groundwater is fresh water found under the ground in the tiny spaces between soil and rocks. It also flows inside special layers of rock called aquifers, which are below the water table. Sometimes, we talk about water that is very close to the surface separately from deeper water that entered the ground a very long time ago.

Role in the water cycle

Further information: Water cycle

Groundwater is part of the water cycle, just like water on the Earth's surface. Water from rain, streams, and rivers can soak into the ground and become groundwater. This process is called infiltration. Once underground, groundwater can flow out naturally through springs or slowly move into oceans.

Groundwater stores a lot of water, much more than water on the surface, and it stays there for a longer time. This makes it easy for people to use groundwater for many years without noticing any problems. However, it's important to use it carefully so it doesn't run out.

Groundwater can stay underground for a very long time, from days up to thousands of years. In places like the Great Artesian Basin in Australia, some groundwater is more than a million years old. Scientists have found that this ancient water moves very slowly, traveling about one meter each year.

Groundwater recharge

Location in aquifers

Characteristics

Temperature

Groundwater stays at a steady temperature because soil and rock protect it from changes in the weather. In some places, groundwater stays around 10 °C (50 °F), which can help keep buildings cool in summer and warm in winter. For example, cool groundwater can be used in homes during hot weather, and warmer groundwater can help heat homes during cold weather.

Availability

Groundwater is a big part of the world's fresh water, making up about thirty percent of all fresh water. It is stored deep underground and can help when there is less water on the surface, like during dry times. Scientists can study groundwater by measuring water levels in wells and looking at rock records from drilling. Different types of rock and soil affect how much groundwater is available, with some areas having more than others.

Uses by humans

Groundwater is very important for people because it is a major source of fresh water used for drinking, growing crops, and many other purposes. About half of the world’s drinking water comes from groundwater, and it also provides a big share of water used for growing food and in factories.

Groundwater is used in many places around the world, especially where there isn’t enough rain. In some countries, like India and China, most of the water for crops comes from groundwater. However, using too much groundwater can cause problems, like running out of water or making the water salty and unsuitable for use. Scientists are studying how climate change might affect groundwater temperatures and availability in the future.

Challenges

Flood protection projects can sometimes reduce natural flooding that helps refill underground water supplies. When too much groundwater is removed over time, the land above can sink, which can damage buildings and roads. In some places, such as coastal areas, pumping too much groundwater can cause salty seawater to move into the fresh water underground, making it unsuitable for use.

Overdraft

Groundwater is very useful, and most places on Earth have some underground water sources. However, in some areas like California, Texas, and India, these water sources are being used up faster than they can refill. This can cause problems such as wells needing to be drilled deeper and can harm plants and animals that depend on groundwater.

Subsidence

When too much groundwater is pumped out, the space left behind can cause the ground to sink. This happens because the underground space that held the water helps support the weight of the land above. When the water is removed, the ground can collapse downward. This sinking can damage buildings and roads and is sometimes permanent.

Groundwater becoming saline due to evaporation

In some places, especially near coasts or in areas with lots of farming, groundwater can become salty. This happens when water evaporates and leaves behind salts, which can then mix into the groundwater. This can make the water unsuitable for drinking or farming if not managed carefully.

Seawater intrusion

Near coastlines, underground fresh water often sits above denser saltwater. If too much fresh water is pumped out, saltwater can move upward into the underground water supplies. This can make the water salty and unsuitable for use. Many coastal areas face this problem, especially where there is a lot of pumping of groundwater.

Pollution

Climate change

Climate change can affect groundwater in several ways. Changes in weather patterns can lead to less water refilling underground supplies or poorer water quality. In some areas, heavier rains might add more water to groundwater, but droughts can reduce it. Rising sea levels can also push saltwater into coastal groundwater supplies. These changes can make it harder to keep water clean and available for people and the environment.

Climate change adaptation

Using more groundwater can help communities prepare for climate change, especially in places where droughts may become more common. Groundwater stores water safely underground, losing less to evaporation than surface water reservoirs. This can help keep water and food supplies stable even when weather becomes more extreme.

Climate change mitigation

Groundwater can also help fight climate change. It plays a role in geothermal energy, which is a clean energy source that produces less carbon dioxide. Some countries use groundwater in heating and cooling systems for buildings. Deep underground layers can also store carbon dioxide, helping reduce the amount in the atmosphere.

Groundwater governance

Groundwater governance helps manage and plan the use of groundwater. It happens at many different sizes and places, including large areas that cross borders.

Managing groundwater focuses on doing practical things every day. Since groundwater is often seen as a private resource connected to land ownership, it can be hard to regulate. Governments play an important role in protecting groundwater because it benefits everyone. Laws and rules control who can use groundwater and how activities might affect its quality. These rules also help protect areas where groundwater comes back into the system and where it is taken out, ensuring it is used in a way that does not run out. In some places, rules for groundwater are made together with rules for surface water, like rivers.

By country

Groundwater is a key water resource for providing drinking water, especially in dry places like arid regions.

In the Arab region, which has very little water, many countries depend heavily on groundwater. However, taking out too much groundwater has caused problems, especially in busy areas with lots of people and farms.