Short answers, pulled from the story.
Water scarcity is the lack of sufficient freshwater resources to meet standard water demand in a region. About four billion people face severe water scarcity for at least one month per year, and half a billion face it all year round. By 2025, a study estimated that 6.2 billion people, roughly 75 percent of the global population, were affected.
Physical water scarcity occurs when natural water resources are insufficient to meet all demands, a problem common in arid regions such as Central and West Asia and North Africa. Economic water scarcity results from a lack of investment in infrastructure or technology to deliver available water to people who need it; the United Nations Development Programme identifies this as the more common form of the problem. About a quarter of the world's population lives under economic water scarcity.
The Falkenmark Water Stress Indicator, developed by Malin Falkenmark, defines water stress as annual water supplies below 1,700 cubic meters per person per year. When supplies fall below 1,000 cubic meters per person per year, a country faces outright water scarcity. The indicator is useful for broad comparisons but does not capture local variations within countries.
The United Nations estimates that only 200,000 cubic kilometers of the total 1.4 billion cubic kilometers of water on Earth is freshwater available for human use. A mere 0.014 percent of all water on Earth is both fresh and easily accessible. Humanity currently uses and reuses approximately 5,000 cubic kilometers of the roughly 14,000 cubic kilometers of easily accessible freshwater.
Water scarcity stems from a mismatch between where water is available and where people need it. Key drivers include population growth, the expansion of irrigated agriculture, industrial water use, climate change, deforestation, and water pollution. Population change has been found to be four times more important than long-term climate change in its effects on water scarcity.
A 2026 report from the UNU Institute for Water, Environment and Health concluded that the terms water stress and water crisis no longer adequately describe the global water situation. The UN adopted the term water bankruptcy to signal both the irreversibility and the insolvency of the current state of water systems.