Beneath the surface of the Earth lies one of our planet’s most precious resources. Most people believe that the water which keeps us alive is found in rivers, lakes and reservoirs. Groundwater rarely gets a mention and yet without it, life would be very different.
When rainwater falls, a number of things can happen to it. Some rainwater enters and replenishes streams, rivers and lakes. Some rainwater is soaked up by plants and vegetation. Some rainwater evaporates and returns to the atmosphere, ready to begin the process all over again.
And some rainwater seeps into the ground. It passes through until it reaches the water table, the point at which the ground below is saturated. All the water in this zone is groundwater – and it plays a huge role in keeping us healthy and prosperous.
How is groundwater formed?
Rainwater is not the only contributor to groundwater. Melting snow or water leaking through the bottom of rivers and lakes into the ground will also become groundwater.
One of the few positives about burst pipes which are left to leak is that they recharge groundwater supplies. Farming can help too. When crops are irrigated with more water than they require, the excess soaks through to the water table.
What is the water table?
Ah yes, the water table. This is the level at which groundwater is first encountered, marking the beginning of the saturated zone.
The water table can rise and fall. During heavy rains, more water soaks into the ground and so the saturated zone starts much closer to the surface. The water table is therefore higher.
On the other hand, an extended period of dry weather will cause the amount of groundwater stored to reduce. With that comes a lowering of the water table.
In regions which experience high levels of rainfall, the water table will naturally be higher. In dry, arid climates it will lie deep in the ground.
Where is groundwater stored?
Groundwater is stored in aquifers, made up of permeable materials capable of storing significant quantities of water.
There are several geological formations which can make up aquifers. The most common include unconsolidated sand and gravel, sedimentary rocks like sandstone and limestone and fractured volcanic and crystalline rocks.
Groundwater does not stand still in aquifers. It will flow, albeit much slower than before it reached the aquifer. If it could not flow, then the materials making up the aquifer would be considered impermeable.
The direction of travel water takes through the aquifer tends to be downwards, governed by gravity. To allow flow to happen, aquifers must have space such as fractures or pores and these must be interconnected.
Extracting groundwater from aquifers
Groundwater can be extracted from aquifers by wells, pumps and boreholes. Once brought to the surface, it can be used for human consumption, irrigation and other processes requiring fresh, clean water.
One of the best examples of the power of groundwater comes from Libya and The Great Man Made River. Vast aquifers were discovered in deserts in the south of the country, containing an estimated 20,000 cubic kilometres of water stored underground since the ice age.
When Muammar Gaddafi and the Free Unitary Officers seized power in the Libyan coup of 1969, the new government immediately nationalised the oil companies.
They then used the revenues coming into the country to drill hundreds of boreholes capable of pumping groundwater to the surface.
This water was transported via a series of pipelines – The Great Man Made River – to the north of Libya, were 80 percent of the population lived along the Mediterranean coast.
For the first time ever, natural drinking water poured out of taps from Tripoli to Benghazi. Gaddafi envisioned going further; he wanted the aquifers and The Man Made River to supply freshwater for farming all over Libya, enabling the country to become self-sufficient by growing enough food to feed its population and then exporting produce to other countries.
The first and second Libyan Civil Wars put paid to those plans, leaving The Great Man Made River to fall into disrepair. Still, it offers a glimpse into the transformative power groundwater and its extraction can have.
The importance of groundwater to world water supplies
Groundwater represents around 30 percent of the planet’s fresh water supply. 69 percent is locked into ice caps, glaciers and mountain snow and just one percent comes from rivers and lakes.
In terms of human consumption, on average groundwater accounts for 33 percent of the fresh water we use. In some parts of the world where rainfall is scarce and there are no natural resources like lakes and rivers, reliance on groundwater can reach 100 percent.
Groundwater quality and health benefits
Groundwater is of the highest quality thanks to its formation process and where it is stored. As it passes through rocks below the surface, it picks up minerals along the way.
There is a reason that bottled water companies boast of the high mineral content of their water – because it is good for you. Calcium, magnesium and other minerals found in groundwater contribute to a healthy diet.
Its storage in layers beneath the surface protects it from contamination and preserves quality. Some groundwater is found at very high levels, such as in mountains and volcanos, offering further preservation and protection.
Groundwater does not require large investments in terms of purifying and treating, unlike processes such as desalination. It can be quickly processed and used by consumers.
The health benefits of groundwater do have one negative, however. Whilst minerals are good for human consumption, they are not so good when passing through pipes.
Hard water as it is known reacts aggressively in pipework, especially when heated through boilers, kettles and other appliances.
This leads to limescale developing and the possibility of real problems. Build up of limescale causes reduced flow, reduced efficiency, impacts on the lifespan of appliances and causes increased energy bills as systems have to work harder to heat properties.
Left untreated, limescale could mean a household find themselves needing to purchase a brand-new boiler or using a pipe repair kit to make an emergency leak repair.
Groundwater and agriculture
Groundwater provides the main source of water for agriculture and the food industry. Irrigation accounts for over 70 percent of combined ground and surface water withdrawal, with groundwater making up 43 percent of that total.
The reason groundwater is so widely used is because of its flexibility. In wet seasons, less groundwater needs to be extracted as rainfall meets the demand.
When it is drier, more can be extracted to meet the production needs of agriculture. Being able to water plants and crops and feed livestock in a cost-effective manner thanks to groundwater gives it a significant role in the economy.