How the global freshwater aquifer system works, and why Australia's groundwater matters

The world's freshwater sits mostly out of sight. About 97 per cent of all fresh water on Earth is frozen or locked in soil and rock. Of the remaining 3 per cent accessible to humans, roughly two-thirds is stored underground in aquifers: vast layers of porous rock and sediment that hold water like sponges. These aquifers are critical infrastructure for food production, drinking water, and industry across every continent. Yet most people never think about them, and many nations are draining them faster than rain and snow can replenish them.

What aquifers are and how they work

An aquifer is simply a geological formation that contains and transmits water. Water from rainfall and rivers percolates down through soil and rock until it reaches an impermeable layer, where it collects. Some aquifers are shallow and refill within years. Others are ancient reservoirs that took thousands of years to accumulate and may not refill for millennia. The water table is the level where groundwater begins. In wet regions, it sits close to the surface. In deserts, it may lie hundreds of metres down. Wells and boreholes tap into aquifers to supply cities, farms, and factories.

Aquifers are not underground lakes or rivers. Water moves through them slowly, measured in centimetres or metres per year. This slow movement filters out many contaminants, making aquifer water generally cleaner than surface water. Yet it also means groundwater responds slowly to pollution, drought, and extraction. A contaminated aquifer can take decades or centuries to recover.

Why aquifers are being drained faster than they refill

Global groundwater use has tripled in the past 70 years. Agriculture accounts for roughly 70 per cent of all groundwater extraction. Modern irrigation feeds the world's growing population, but it depends entirely on aquifers in many regions. The Indus Basin in South Asia, the North China Plain, and the US Great Plains are three of the world's most productive agricultural zones. All three are mining their aquifers: extracting more water than annual rainfall replenishes. Fossil aquifers, like the Nubian Sandstone beneath the Sahara, are essentially non-renewable once depleted. Even renewable aquifers can cross a threshold where overpumping causes collapse. As water levels fall, wells require more energy to pump, costs rise, and marginal farmland becomes uneconomic. Communities that depend on a single aquifer face the prospect of drying up altogether.

Climate change intensifies the problem. In many regions, rainfall is becoming less predictable. Droughts last longer. Snowmelt arrives earlier or in reduced volume. This shifts more pressure onto groundwater reserves. Some aquifers are also being polluted by fertiliser runoff, industrial discharge, and salt intrusion from over-extraction near coasts.

How aquifers cross borders and create conflict

Many of the world's largest aquifers are transboundary. They supply water to multiple nations with no formal agreement on how to share it. The Nubian Sandstone aquifer lies beneath Egypt, Sudan, Chad, and Libya. The North Western Sahara Aquifer underlies Algeria, Morocco, and Tunisia. The Guarani Aquifer spans Argentina, Brazil, Paraguay, and Uruguay. When one nation pumps heavily, it affects water availability downstream. Unlike surface water treaties, which are more common, groundwater agreements are rare and often poorly enforced. Disputes over aquifer depletion risk becoming sources of conflict as populations grow and climate change reduces other water sources.

What it means for Australia

Australia holds some of the world's largest and most ancient aquifers, including the Great Artesian Basin, which spans Queensland, New South Wales, South Australia, and the Northern Territory. For over a century, this resource has supported agriculture, mining, and rural communities. Yet the Basin is being drawn down faster than it recharges. Climate variability means dry spells put acute pressure on groundwater. In the Murray-Darling Basin, Australia's agricultural heartland, unsustainable groundwater extraction has contributed to river decline and ecosystem damage. As a wealthy nation with developed water infrastructure, Australia is better positioned than most to manage aquifer depletion. Yet the same pressures facing other countries are present here: food production depends on groundwater, climate is becoming less predictable, and competing users struggle to agree on sustainable extraction limits. Australia's experience with aquifer management influences policy discussions across the Indo-Pacific region, where groundwater stress is driving migration, political tension, and food insecurity.

The bottom line

Aquifers are invisible infrastructure that supply half the world's population with drinking water and irrigation for much of its food. Many are being depleted faster than nature refills them. Without coordinated management, aquifer collapse will reshape where people can live and farm, intensify conflicts between nations, and destabilise food systems. Australia's groundwater is not infinite. Protecting it requires understanding that these hidden reserves are shared resources whose stewardship affects communities far beyond our borders.

This article was compiled by AI and screened before publishing. See our editorial standards.