Every human life, household, and community on the planet is sustained by water - to bathe, to grow food, and of course, to drink.
And now, a new global report says, humanity is starting to run out of it.
The report from the United Nations says the world has moved past more familiar terms such as "water stressed" and "water crisis", and has entered "global water bankruptcy".
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This new era is marked by irreversible losses of water supplies, and an inability to rebuild them.
"This report tells an uncomfortable truth: many regions are living beyond their hydrological means, and many critical water systems are already bankrupt," lead author Kaveh Madani, director of the UN's Think Tank on Water, said.
Glaciers are vanishing, wetlands and lakes are drying up, and long-term aquifers are shrinking.
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While not every basin and country is water-bankrupt, Madani says, "enough critical systems around the world have crossed these thresholds".
"These systems are interconnected through trade, migration, climate feedbacks, and geopolitical dependencies, so the global risk landscape is now fundamentally altered," he said.
Madani said that the worsening climate crisis and water loss were interrelated, and action on one would also help mitigate the other.
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He also urged the world to use the crisis as a bridge of unity, noting that water "crosses traditional political boundaries" and could be used as a powerful focus of co-operation.
It's an optimistic outlook compared to some other observers, who have suggested that water reserves could become the focus of political dispute and military action in the near future.
Major hotspots include the Middle East and northern Africa, parts of South Asia, and even the US South-West.
Australia is not mentioned in the report, but is experiencing ongoing drought in parts of the country's south and fears for the health of the Murray River system.
By the numbers, 75 per cent of humanity are now living in water-insecure countries, while 2.2 billion people around the world lack safely managed drinking water.
Half the world's large lakes, on which the UN says 25 per cent of humans "directly" depend, have lost water since the 1990s.
And 70 per cent of the world's major aquifers show long-term decline.
"Millions of farmers are trying to grow more food from shrinking, polluted, or disappearing water sources," Madani said.
"Without rapid transitions toward water-smart agriculture, water bankruptcy will spread rapidly."
The report also warns that a radical new global approach is needed, focusing on water monitoring, agricultural reform, and environmental protection.
He warned some communities would see a "transition" in their way of life and governments should support them through that.
"Water bankruptcy is becoming a driver of fragility, displacement, and conflict," UN Under-Secretary-General Tshilidzi Marwala said.
"Managing it fairly – ensuring that vulnerable communities are protected and that unavoidable losses are shared equitably – is now central to maintaining peace, stability, and social cohesion."
Madani said despite the alarming results of the research, the report was not putting forward a "hopeless" situation.
"Declaring bankruptcy is not about giving up, it is about starting fresh," he said.
"By acknowledging the reality of water bankruptcy, we can finally make the hard choices that will protect people, economies, and ecosystems. The longer we delay, the deeper the deficit grows."
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