Water shortages happen when demand for freshwater outpaces what nature and infrastructure can supply. The causes are layered: climate change is reshaping where rain falls, population growth is concentrating demand in cities, agriculture consumes the vast majority of available freshwater, and pollution renders much of what remains unusable. No single factor explains the crisis. It’s the collision of all of them at once.
Most Freshwater Goes to Farming
Agriculture accounts for roughly 72 percent of all freshwater withdrawals worldwide. That includes irrigation for crops and water for livestock. In arid regions where food production depends heavily on irrigation, rivers and underground aquifers are being drained faster than rainfall can refill them. The Aral Sea in Central Asia, once one of the world’s largest lakes, shrank dramatically over decades largely because the rivers feeding it were diverted for cotton farming.
As the global population grows and diets shift toward more water-intensive foods like meat and dairy, agricultural water demand keeps climbing. Industrial and domestic use together make up the remaining 28 percent, but even modest increases in those sectors compound the pressure on the same limited supply.
Climate Change Is Rearranging the Water Cycle
Rising temperatures speed up evaporation from soil, lakes, and rivers. More evaporation means more moisture in the atmosphere and more precipitation globally, but that rainfall isn’t distributed evenly. Some regions get heavier storms and flooding while others dry out. Traditional rain belts and desert boundaries are shifting, so places that historically had reliable water are losing it, and places getting more rain often can’t capture or store the excess.
Warmer air also pulls moisture from soil faster, which means even areas that receive the same amount of rain can end up drier because the ground loses water between storms. Snowpack, which acts as a natural reservoir in mountain regions, is melting earlier in the year. Communities that depend on slow spring snowmelt for summer water supply are finding that the water arrives too early, runs off before it’s needed, and leaves rivers low during peak demand months.
Cities Are Growing Faster Than Water Systems
The world’s urban population jumped from 0.8 billion in 1950 to 4.4 billion in 2020 and is projected to reach 6.7 billion by 2050. That concentration of people creates enormous local demand. In 2016, roughly 933 million city dwellers already faced water scarcity. By 2050, that number is projected to reach between 1.7 and 2.4 billion, with India expected to see the sharpest increase, adding between 153 and 422 million people to its water-scarce urban population.
Urban industrial and domestic water demand alone is expected to rise 50 to 80 percent over the next three decades. Many of the fastest-growing cities sit in regions that were never water-rich to begin with. Building the infrastructure to deliver clean water to rapidly expanding neighborhoods takes massive investment, and low- and middle-income countries often can’t keep pace. The number of large cities exposed to water scarcity is projected to grow from 193 to as many as 284, including 10 to 20 megacities of 10 million people or more.
Pollution Shrinks the Usable Supply
Not all water shortages are about quantity. Contamination effectively removes water from the available supply even when rivers and lakes look full. Nutrient pollution from agricultural runoff, particularly nitrogen and phosphorus from fertilizers and animal waste, is one of the biggest culprits. In the United States, roughly half of all bodies of water are impaired by excess nutrients. That pollution can make water undrinkable, kill aquatic life, and fuel toxic algal blooms that close off reservoirs.
Industrial discharge, untreated sewage, and chemical contamination create similar problems worldwide. The Clean Water Act in the U.S. set goals in the 1970s for all streams and rivers to be fishable, drinkable, and swimmable within roughly a decade. Those goals have not been met, particularly for nutrient pollution from diffuse sources like farm fields and urban stormwater that are harder to regulate than a single factory pipe. In developing countries, the situation is often worse because wastewater treatment infrastructure is limited or nonexistent.
Leaking Pipes Waste What’s Already Treated
Even after water is collected, treated, and pumped into distribution systems, a significant portion never reaches a tap. In Western Europe, water losses from leaking infrastructure average around 12 percent. In North America, the benchmark is about 15 percent. In developing countries, non-revenue water (water that’s treated and distributed but lost to leaks, theft, or metering errors) averages around 20 percent and often runs much higher in individual cities.
Aging pipes, deferred maintenance, and insufficient funding for upgrades all contribute. In some older systems, a quarter or more of treated water seeps into the ground before anyone can use it. Fixing these losses is one of the more straightforward ways to stretch existing supply, but it requires sustained investment that many municipalities struggle to prioritize against other needs.
Countries Are Fighting Over Shared Rivers
About 60 percent of the world’s freshwater flows through river basins that cross national borders. When an upstream country builds a dam, diverts a river, or expands irrigation, it can directly reduce the water available downstream. These conflicts take two forms: downstream nations pushing to secure a larger share of upstream flow, and upstream nations asserting control over runoff through storage or diversion projects.
The Nile is one of the most prominent examples. International disputes flared in 2020 when Ethiopia began filling the Grand Ethiopian Renaissance Dam, alarming Egypt and Sudan, which depend on the Nile for the vast majority of their water. Similar tensions exist between the U.S. and Canada, where Montana has called for renegotiating water-sharing agreements, claiming Canadian farmers are overusing shared resources. As climate change reduces flow in many of these rivers, the competition for what remains is intensifying.
Desalination Helps but Has Limits
The ocean holds 97 percent of Earth’s water, so converting saltwater to freshwater seems like an obvious fix. Modern reverse osmosis plants can produce drinkable water using about 3.5 kilowatt-hours of electricity per cubic meter, with distribution pushing that closer to 4. That’s a significant energy cost, especially at the scale needed to supply a city. Older thermal desalination methods use far more, roughly 38 to 100 kilowatt-hours of thermal energy per cubic meter depending on the technology.
The energy requirement means desalination is expensive and, if powered by fossil fuels, carbon-intensive. A gas-powered desalination plant produces around 1,700 grams of CO2 per cubic meter of water. Coal pushes that to 2,900 grams. Nuclear-powered reverse osmosis drops the footprint to about 50 grams. Desalination is expanding in wealthy, water-scarce countries like Saudi Arabia, Israel, and Australia, but for most of the world, the cost and energy demands remain prohibitive at scale. Treating brackish water or recycling municipal wastewater through reverse osmosis is far cheaper, requiring only about 1 kilowatt-hour per cubic meter, and is gaining traction in many regions as a more practical alternative.
Why It’s Getting Worse, Not Better
Water scarcity isn’t a single problem with a single cause. It’s the result of overlapping pressures that reinforce each other. Climate change reduces reliable supply in many regions while increasing demand for irrigation. Population growth concentrates that demand in cities where infrastructure can’t keep up. Pollution removes water from the usable pool. Leaking systems waste what’s already been treated. And geopolitical competition makes cooperation on shared rivers harder.
More than two thirds of water-scarce cities could technically relieve their shortages through infrastructure investment, including better pipes, wastewater recycling, and improved efficiency. The barrier is less about technology than about money, political will, and the speed at which systems can be built. The gap between what’s needed and what’s being done is why water shortages are projected to affect nearly half the world’s urban population within the next 25 years.