Water. As the population grows, there are more and more people at the tap every day. But when it comes to the world’s demand for water, drinking it is just the beginning

“Food - and agriculture in particular - is by far the largest user of water,” says Pasquale Steduto, the head of water programs at the UN Food and Agriculture Organization.

Agriculture accounts for 70 percent of the water drawn from rivers and aquifers worldwide.

So, while each person drinks about two to three liters of water per day, it takes roughly 200 liters to produce that person’s daily diet of maize. Bread takes 270 liters. Rice? 420. And the meat to go with it takes even more water. Pork: 930 liters for a day’s serving. Lamb: 1400 liters. And beef is the thirstiest of all: 2400 liters.

And the demand for water is growing along with the demand for food.

“We are expecting another two billion, if not more, people coming in the next 40 years," Steduto says. "We are already in a situation of water-scarce conditions." 

Water is scarce in some places because farmers are pumping it out of the ground faster than it can recharge, according to the head of water policy for the US State Department, Aaron Salzberg.

“The groundwater is getting depleted to the point where that will have an impact on food security," he says. "If you look at India, for example, in the breadbasket up in the northwestern part of the country, over-extraction is a huge, huge issue and this is going to start to play a role in their ability to produce food and to meet their internal needs.”

Over-extracting groundwater for irrigation is also a huge issue in major farming regions of China, the United States and elsewhere.

On the other hand, much of sub-Saharan Africa has the opposite problem: not enough irrigation. Most African farmers depend on rainfall, which is becoming less reliable with climate change.

"This rainfall is not being predictable, putting the land at higher risk," says Steduto, "so we cannot predict or anticipate how much food we are going to produce.”

Producing more food for more people with less water in the coming years will be a challenge. 

But there are solutions. Low-tech treadle pumps for farmers who need irrigation. Drip irrigation for farmers who need to squeeze more crop per drop. And eating less meat in countries that already overconsume it, just to name a few.

“We know how to do it. We need to make this into practice," says Steduto, "so, from that side, that we have a solution, I am optimistic.”

But making changes takes time. And Steduto is less optimistic about the pace of change. So is the State Department’s Aaron Salzberg.

“I think it’s the lack of political will," Salzberg says. "The fact that governments just haven’t made the decision to make this a priority.”

But experts say that making that decision may no longer be up to those governments, as climate change threatens water supplies already stressed by a growing population.