Scientists are concerned about freshwater because the supply is far smaller and more fragile than most people realize, and nearly every pressure on it is intensifying at once. Only about 0.5% of all water on Earth is accessible fresh water. The rest is saltwater, locked in glaciers and ice caps, or trapped too deep underground to reach affordably. That narrow sliver supports all human drinking water, agriculture, industry, and the freshwater ecosystems that billions of species depend on.
The Supply Is Tiny and Unevenly Distributed
While 3% of Earth’s water is technically fresh, the vast majority of that is unavailable. Glaciers, polar ice, atmospheric moisture, and deep soil hold about 2.5% of the planet’s total water. What remains for lakes, rivers, and reachable aquifers is roughly half a percent. Rivers alone account for just 0.0001% of all water on Earth, and freshwater lakes hold only 0.009%.
That small supply also isn’t spread evenly. Some regions have far more renewable fresh water per person than they need, while others fall well below recognized stress thresholds. Hydrologists generally consider a population water-scarce when it has less than 1,700 cubic meters of renewable fresh water per person per year. Below 1,000 cubic meters, conditions qualify as water stress. Below 500, a region faces absolute water stress, where basic needs and food production become difficult to sustain simultaneously.
Demand Is Growing Faster Than Supply
In 2016, roughly 933 million people living in cities faced water scarcity. Projections published in Nature Communications estimate that number will climb to between 1.7 and 2.4 billion urban residents by 2050, more than doubling in just over three decades. India is expected to bear the worst of that growth, with an additional 153 to 422 million city dwellers pushed into water-scarce conditions.
Agriculture is the single largest consumer. Farming accounts for 72% of all freshwater withdrawals worldwide, according to the UN’s Food and Agriculture Organization. Industry uses about 16%, and municipal services (drinking water, sanitation, hospitals) take the remaining 12%. As populations grow and diets shift toward more water-intensive foods like meat and dairy, agricultural demand is expected to keep rising.
Underground Reserves Are Being Drained
When surface water runs short, communities turn to groundwater. But many of the world’s major aquifers are being pumped faster than rainfall can refill them. The High Plains Aquifer in the central United States, one of the most productive agricultural aquifers on Earth, has lost roughly 330 cubic kilometers of water since large-scale irrigation began in the 1950s. That represents about 8% of the groundwater that was available before pumping started. California’s Central Valley has lost an estimated 140 cubic kilometers over a similar timeframe.
In northwest India, satellite measurements show groundwater dropping at a rate of about 14 cubic kilometers per year. These losses are essentially irreversible on any human timescale. Aquifers that took thousands of years to fill are being emptied in decades, and once they’re gone, the land above them can compact permanently, reducing the aquifer’s capacity to hold water even if rainfall eventually returns.
Saltwater Is Pushing Inland
Coastal communities face a different kind of loss. Beneath every coastline, underground fresh water and seawater naturally push against each other, held in balance by opposing pressures. Climate change is disrupting that balance from both directions. Rising sea levels increase the force driving saltwater inland, while reduced rainfall in some regions weakens the flow of fresh water pushing back toward the ocean.
A NASA and Department of Defense study evaluating more than 60,000 coastal watersheds worldwide found that saltwater will infiltrate freshwater aquifers in about three out of every four coastal areas by 2100. Rising seas alone would affect 82% of the watersheds studied. Once saltwater contaminates a freshwater aquifer, the water becomes unusable for drinking or irrigation without expensive desalination.
Pollution Is Shrinking Usable Supplies
Even water that hasn’t been physically depleted can become unusable. Globally, about 48% of all wastewater is released into the environment without any treatment. That raw sewage, along with industrial discharge and agricultural runoff carrying pesticides and fertilizers, degrades rivers, lakes, and shallow groundwater that communities depend on.
A newer class of pollutants has added urgency to the problem. Synthetic chemicals known as PFAS, sometimes called “forever chemicals” because they don’t break down naturally, have been detected in freshwater systems around the world. These compounds, used in nonstick coatings, waterproof fabrics, and firefighting foam, persist in water indefinitely and accumulate in the body over time. The EPA set its first enforceable limits for PFAS in drinking water in 2024, capping two of the most common varieties at just 4 parts per trillion. To put that in perspective, one part per trillion is roughly equivalent to a single drop of water in 20 Olympic swimming pools. The health-based goal for those two chemicals is zero, meaning no amount is considered truly safe. Cleaning PFAS out of water supplies requires advanced filtration that many utilities don’t yet have.
Freshwater Ecosystems Are Collapsing
The damage isn’t limited to human water supplies. Freshwater ecosystems, including rivers, lakes, wetlands, and the species that live in them, are declining faster than any other major habitat type on Earth. Monitored populations of freshwater vertebrates (fish, amphibians, reptiles, mammals, and birds that depend on freshwater habitats) declined by an average of 84% between 1970 and 2016, according to WWF’s Living Planet Report. That rate is dramatically worse than the 68% average decline seen across all wildlife populations globally over the same period.
Freshwater species are squeezed from every direction: dams fragment rivers, pollution degrades water quality, invasive species outcompete native ones, and water withdrawals reduce the flow that habitats need to function. Wetlands, which naturally filter pollutants and buffer floods, have been drained or degraded across much of the world. Losing these ecosystems doesn’t just threaten biodiversity. It removes natural water purification and flood control that would cost enormous sums to replace with engineered systems.
Climate Change Compounds Every Problem
What ties these concerns together is climate change, which acts as a threat multiplier. Warmer temperatures increase evaporation from reservoirs and soil, meaning more water is lost before it can be used. Shifting precipitation patterns are making wet regions wetter and dry regions drier, intensifying both floods and droughts without increasing the total usable supply. Glaciers that feed major rivers in Asia and South America during dry seasons are shrinking, threatening the water security of hundreds of millions of people who depend on that meltwater.
Droughts are lasting longer and becoming more severe in many regions, reducing the recharge that replenishes both surface water and aquifers. At the same time, when rain does fall, it increasingly comes in intense bursts that run off hardened or saturated ground rather than soaking in. The net result is that even areas with stable total rainfall may end up with less usable water.
Scientists are concerned because these pressures are not isolated. Groundwater depletion, pollution, ecosystem collapse, saltwater intrusion, and rising demand are happening simultaneously, each making the others harder to solve. The window to manage freshwater sustainably is narrowing, and the resource itself cannot be manufactured or substituted.