(CNN)Almost 5 billion people could struggle with water shortages by 2050 due to climate change, according to the United Nations.
5 everyday foods that are making droughts worse
Already, more than 25% of the world's crops are grown in regions with severe water shortages, according to the World Resources Institute.
In many countries, farmers tap into groundwater to irrigate their crops, particularly during periods of limited rainfall, and experts warn that irrigation is contributing to water shortages in drought-prone regions.
Here, we look at five everyday water-intensive foods that are using precious water in areas where it is in short supply.
Aabout 80% of the world's almonds are grown in California. A recent study found that between 2004 and 2015, it took an average of 12 liters of water to grow just one Californian almond, and almond farmers rely heavily on irrigation and groundwater reserves to water their crops.
Almond production uses around 2 trillion liters of water per year and is contributing heavily to groundwater depletion and land degradation, according to Professor Yoshihide Wada, deputy director of the water program at the International Institute for Applied Systems Analysis.
Groundwater levels in the Central Valley, where most almond crops are grown, dropped by almost a half-meter annually during California's historic seven-year drought in 2011, according to a study by Cornell University.
"It is unsustainable," Wada said, adding that almond prices could rise if farmers keep pumping deeper to reach groundwater. "It's economically unprofitable if you go too deep."
Many almond farmers are taking steps to cut water use, for example by using micro-irrigation systems, which apply water directly to tree roots.
The Almond Board of California says that by 2025, the California almond community commits to reduce the amount of water used to grow a pound of almonds by an additional 20%.
It takes an average 2,000 liters of water, 10 full bathtubs, to grow just one kg of avocados, according to the Water Footprint Network, a Dutch organization that advocates for better management of water resources.
The brunch favorite's water consumption is four times the amount needed to produce the same amount of oranges or a kilogram of tomatoes, according to the network.
In the past decade, global avocado imports increased by more than 10% annually, according to Wada. Increased demand put a strain on drought-stricken farmers in the Chilean province of Petorca, who resorted to overpumping groundwater and diverting water from emptying rivers, he said.
In arid Petorca, every cultivated hectare of avocados requires 100,000 liters of irrigated water a day, according to WaterAid.
"Avocado trees are perennial crops, which require water year-round. Irrigation is the only way to sustain rapidly growing avocado production and exports," Wada said.
Avocado farmers' reliance on irrigation and climate change could compromise food security in the region, according to Wada.
"With climate change, future water supply is uncertain due to more extreme weather events. Water is being used for a short-term economic interest, but long-term management is needed to sustainably use the water resources," he said.
"Sugarcane is one of the most water-intensive crops," according to Wada.
It takes an average of 210 liters of water to produce one kg of sugarcane. The water footprint of refined sugar is 1,780 liters of water, nine full bathtubs, per kilogram, according to the Water Footprint Network.
In 2017, the former deputy executive director of the UN Environment Programme said that there was "absolutely no justification in Pakistan for sugarcane."
"Sugarcane is like growing trees, like growing a forest, in the amount of water it consumes. And the rate of recovery, the amount of sugar you get from a liter of sugarcane juice is the lowest in the world," Shafqat Kakakhel said.
In Pakistan, 80% of the water supply for sugarcane comes from irrigation and groundwater reserves, according to the Water Footprint Network.
Government subsidies for groundwater extraction mean farmers do not view water as a "precious resource," said Jamison Ervin, head of the Nature for Development Program at the United Nations Development Program.
India is the world's leading rice exporter, but in some parts of the country, growing rice is using up groundwater faster than it can be replenished.
Rice uses 1,670 liters of water, eight full bathtubs, per kilograms, according to the Water Footprint Network.
Last year, Columbia University-led research said many parts of India experience "chronic water stress due to heavy-water extraction for irrigated agriculture," noting that in the states of Punjab and Haryana in particular, rice growing is demanding increasing amounts of irrigation.
According to nonprofit WaterAid, India's rate of groundwater depletion increased by 23% between 2000 and 2010. India uses more groundwater than anywhere in the world -- 24% of the global total -- and 1 billion people there live in water-scarce areas.
The Indian government subsidizes diesel electric pumps, allowing farmers to continue pumping groundwater during periods of limited rainfall, Wada said, adding that the next two decades are a "critical" time for the country to reduce its water shortages.
The Columbia researchers suggested that in some parts of India, planting alternative cereals, including sorghum, maize and millet, could provide more nutrition than rice for the amount of water they consume.