The world will have only 60% of the water it needs in just 15 years unless countries dramatically change their use of the resource, a UN report warns.

World Water Day 2015
June 1, 2003: People gather to get water from a huge well in the village of Natwarghad in the western Indian state of GujaratAmit Dave/Reuters

Many underground water reserves are already running low, while rainfall patterns are predicted to become more erratic with climate change. As the world's population grows to an expected nine billion by 2050, more groundwater will be needed for farming, industry and personal consumption.

The report predicts global water demand will increase 55% by 2050, while reserves dwindle.

World Water Day 2015
April 4, 2013: Bottles tied to ropes are lowered into an almost dry well in Bhaktapur, NepalNavesh Chitrakar/Reuters
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March 20, 2013: A villager carries buckets of water from a polluted stream which is used for his daily drinking water, in Dongchuan district of Kunming, Yunnan province, ChinaReuters
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January 7, 2014: Displaced people carry water containers on their heads at Tomping camp, near South Sudan's capital JubaJames Akena/Reuters
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December 13, 2011: A woman collects a sample of red polluted water flowing from a sewer into the Jian River in Luoyang, north China's Henan provinceAFP

Having less water risks catastrophe on many fronts: crops could fail, ecosystems could break down, industries could collapse, disease and poverty could worsen, and violent conflicts over access to water could become more frequent.

"Unless the balance between demand and finite supplies is restored, the world will face an increasingly severe global water deficit," the annual World Water Development Report said, noting that more efficient use could guarantee enough supply in the future.

World Water Day 2015
October 14, 2008: Children bathe in waste water at a slum in Jakarta, IndonesiaBeawiharta/Reuters
World Water Day 2015
June 13, 2003: A man climbs out of a well with a seven-litre rubber pouch strapped on his back to fetch a days' supply of drinking water for local residents in the village of Chuda Chokadi in Gujarat state, IndiaAmit Dave/Reuters
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May 26 2003: A girl collects water from a hole in the ground in the Tariq district of the Saddam city neighbourhood of BaghdadKieran Doherty/Reuters
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September 27, 2012: Styrofoam food containers clog a canal in Port-au-Prince, HaitiSwoan Parker/Reuters
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July 1, 2012: A girl uses a submerged hand-pump to fetch drinking water during floods at Dhuhibala village in the north-eastern Indian state of AssamUtpal Baruah/Reuters
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March 22, 2012: A young girl fetches murky water from a hole dug near a dried-up well in Jamam, South SudanHannah McNeish/AFP

The report, released before World Water Day 2015, calls on policymakers and communities to rethink water policies, urging more conservation as well as recycling of wastewater. Countries may also want to consider raising prices for water, as well as searching for ways to make water-intensive sectors more efficient and less polluting, it said.

About 748 million people worldwide have poor access to clean drinking water, the report said, cautioning that economic growth alone is not the solution – and could make the situation worse unless reforms ensure more efficiency and less pollution.

World Water Day 2015
June 12, 2009: A boy drinks water from a pond in Bule Duba village, near the edge of Oroma and Somali regions of EthiopiaIrada Humbatova/Reuters
World Water Day 2015
December 10, 2011: A girl from the war-torn Blue Nile state collects water from a muddy pond in South Sudan's Doro refugee campHereward Holland/Reuters
World Water Day 2015
April 16, 2011: Villagers carry pitchers filled with drinking water after visiting a well at Meni village in the western Indian state of GujaratAmit Dave/Reuters
World Water Day 2015
August 9, 2010: A man, marooned by flood waters along with his his livestock, waves towards an army helicopter for relief handout in the Rajanpur district of Pakistan's Punjab provinceReuters
World Water Day 2015
March 19, 2015: A father and son on a makeshift boat made from styrofoam paddle through a garbage-filled river as they collect plastic bottles to sell in ManilaNoel Celis/AFP
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March 22, 2014: Women collect drinking water from the dried-up bed of the Siang River at Berasapori village, some 560 kms from Guwahati, the capital city of India's north-eastern state of AssamBiju Boro/AFP
World Water Day 2015
July 11, 2007: A worker clears away dead fish at a lake in Wuhan, central China's Hubei provinceReuters

World Water Day has been observed on 22 March every year since it was established by the UN General Assembly in 1993.

The idea is to make people think twice about how much water they waste. People who have plentiful access to water are encouraged to try not turning on their taps all day.

World Water Day 2015
March 13, 2008: Residents crowd for water at the only standpipe in Mabella slum in Sierra Leone's capital FreetownKatrina Manson/Reuters
World Water Day 2015
March 21, 2010: A man wraps a cloth around himself after a ritual dip in the polluted Yamuna river in New DelhiDanish Siddiqui/Reuters
World Water Day 2015
March 21, 2010: A man washes clothes in a polluted pond in Xiangfan, Hubei province, ChinaReuters
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March 25, 2010: A villager walks past a dried-up pond in the drought-hit Shilin County of Kunming, Yunnan province, ChinaReuters