Water is the most abundant natural resource when it comes to volume. Yet only 3% of the available water is drinkable and suitable for humans, animals, and agriculture. This is an alarming fact if we consider the increasing world population and uneven demography. Many regions depend solely on groundwater extraction to supply their population.
While aquifers are renewed through the hydrologic cycle, this process can take years. In this context, finding a balance between extraction and replenishment is vital to keep this supply available in the near future.
Main freshwater sources
The freshwater sources have been decreasing as the population increased and agriculture developed. In the past decades, environmentalists and scientists have warned us about the dangers of water supply misuse. Statistics published by the World Bank show a dramatic decline in water supply per capita from 1965 to 2015. In half a century, freshwater resources decreased from roughly 13.5 million cubic meters to less than 6 million.
One-quarter of the world’s freshwater comes from aquifers. The rest is found in glaciers, lakes, rivers, and atmospheric vapor. Groundwater withdrawal is one of the most accessible freshwater sources for human beings. These reservoirs are formed through the hydrologic cycle: evaporation, condensation, precipitation, and infiltration.
Hence, the water that’s not evaporated penetrates through the surface and travels across the subsoil layers, forming large ‘water pools’. Nowadays, these are estimated to be 10-million-km3 long. Although groundwater may be the solution to the water crisis, there are still many issues to resolve.
Structural problems of groundwater mining
Scientists are facing many challenges concerning groundwater and its withdrawal methods. Overuse and depletion of these underground pools can cause the following issues:
- Lowering of the water table
- Land subsidence
- Higher costs
- Reduction of other water supply sources like surface water
- Decreased water quality
The depletion of groundwater resources is a major concern and it’s already visible in some regions like the United Arab Emirates, India, and California in the US. Due to the climate conditions, these regions are heavily dependent on groundwater to support agriculture.
We haven’t been able to find accurate statistics about Africa, but groundwater misuse in this continent is a major concern, especially in large cities. Boreholes and wells are increasingly being used both for domestic uses and industrial purposes.
Next, we analyze the above-mentioned consequences of groundwater withdrawal misuse.
Lowering of the water table
This can create water shortages and cause some wells to dry. Hence, water must be pumped from deeper wells or boreholes that extract water from below the water table. This generates higher withdrawal costs and causes land subsidence.
Land subsidence
Excessive withdrawal without proper replenishment can decrease the water level of aquifers. This causes the land to subside, endangering buildings and town infrastructure. The lower water level affects the soil’s inner structure, causing many issues like pipe damaging, sinkholes, and cracking house walls.
The next piece of news states that the ground in San Joaquin Valley, California, is decreasing by 1 foot a year.
Higher costs
As the water table decreases, extraction becomes more difficult. Owners will have to deepen their wells or create new ones to be able to reach their water supply. In the case of boreholes, they will require more energy to be able to pump the water all the way to the surface. This causes a significant increase in power, resources, and expenses.
Reduction of surface water
Excessive pumping can lead to changes in ecosystems. Aquifers are connected to surface water sources, therefore, significant changes in groundwater levels can affect the water flows of lakes, streams, and even wetlands. Also, the surface water level can be reduced significantly.
Decreased water quality
Depletion of groundwater in coastal areas can cause a saltwater intrusion into the confined aquifers. This would ruin a major source of freshwater mainly used by corporations and industrial miners. Another alarming issue is the unregulated construction of wells and boreholes. If the water supply is contaminated by gasoline, chemicals, or septic tanks, it can cause epidemics and other health hazards.
Groundwater depletion and replenishment: a complex case
The water level reduction of aquifers is a complex matter. While many people think that aquifers are plain underground pools that cover a large extension, this is not always the case. In such a geographic disposition, the water level is reduced evenly and replenished through precipitations anywhere across the area. Thus, all residents have the same access to recharged sources. They also share the same shortage issues.
Yet, other types of soil conditions generate different kinds of aquifers. Some of them have been created by a complicated rock structure and layers of different permeability. This created underground reservoirs of different depths, sizes, dispositions, and volumes.
Under such conditions, the rainfall reloads are not shared equally by all landowners. Due to the complex soil characteristics, permeability variations, and connecting pathways, the alteration of water level is hard to measure or even predict.
It becomes difficult to compare the water sources from wells in proximity. While one neighbor may have plenty of water available, the other may experience a shortage. This is because they are drawing from different depths. Even if they are pumping at the same depth, the soil may have dissimilar permeability. In such conditions, it’s hard to estimate if one neighbor’s usage is affecting the other neighbor’s supply.
The same applies to recharging rates. The permeability of a rock is measured by its capacity to let water pass. The more permeability, the easier it’s for water to travel across the ground and reach the aquifer. In this scenario, it’s almost impossible to estimate supply levels in the future and lay out a provisioning strategy.
Final thoughts on the issues of groundwater mining
There are millions of cubic kilometers of freshwater lying below us. Although groundwater extraction is a promising approach, there are still many issues to resolve and challenges to overcome.
One thing remains clear: If humans don’t find a way to balance the withdrawal/replenishment ratio, we risk endangering yet another valuable source for our survival.