Within 15 years, the world water supply will fall short by at least 40 percent, a United Nations report cautioned Friday.

Released on World Water Day, the discusses trends in water use and predicts a dwindling supply in areas like sub-Saharan Africa and Southeast Asia.

The report says a handful of factors are working in concert to constrict the already-contested water supply in developing countries: unchecked population growth, urbanization and industrialization.

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"Unless the balance between demand and finite supplies is restored, the world will face an increasingly severe global water deficit," the report says.

Climate change can also have a negative effect on the water supply.

Temperature increases cause higher evaporation from open freshwater sources, dwindling the supply. Coastal erosion brings seawater into aquifers, forcing governments to fund expensive desalination, the report says.

A population explosion, however, is the big culprit.

By 2050, the U.N. projects the global population at 9.1 billion people. According to the report, however, the relationship between water use and population growth isn't linear. In fact, over the last few decades, the rate of demand for water is double the rate of population growth.

Although the report projected with an international focus, the struggle for water hits hard at home, too.

A day before the U.N. released its report, California Gov. Jerry Brown rolled out a plaguing the state.

Four years into the drought, Californians face tightened water restrictions that limit when and where they can harness water supplies.

MORE ON WEATHER.COM: California Drought 2015