The world's water resources are being depleted at an alarmingly fast rate and world leaders must do more to preserve water through improved water efficiency in agriculture, an expert with a leading environmental group has urged.

"What we are seeing is a trend of increasing depletion of the world's water resources and the scarcity of water is increasingly becoming an issue of national security for many countries," Brian Richter, director of the Nature Conservancy's Global Freshwater Program, told Xinhua in an interview.

It's increasingly urgent that governments across the world step up measures to help reduce that rate, particularly by making the world's production of food crops more water-efficient, he said.

As nations across the globe prepare to celebrate the 2012 World Water Day, the Washington-based Nature Conservancy, a leading international conservation organization, released a report showing that 2.7 billion people across the world are affected by water shortages on a regular basis.

The eye-opening report, of which Richter is one of the authors, also shows that it is getting very difficult to meet water needs in more than half of the river basins in the world.

This Thursday, March 22, is World Water Day, an event established by the United Nations in 1993 to highlight the challenges associated with this precious resource. Each year has a theme and this year's is "Water and Food Security: The World Is Thirsty Because We Are Hungry."

Food production is the place to start in order to solve the water problem, because as much as 92 percent of the water depletion in the world, according to the study, is linked to the increasing pressure on farmers to produce crops in areas with limited rainfall.

"In the study we found that 92 percent of the water depletion globally is tied to agriculture and agriculture is by far the most dominant use of water that leads to the depletion of the world's water from rivers, lakes and ground water," said Richter.

"We don't want to make farmers the villains here because we need the food they produce, but we have to help farmers produce more and produce more efficiently with less water," he said.

The most pressing need is to help farmers switch traditional agricultural practices into using state-of-the-science irrigation methods and improve the productivity of rain-fed farms as soon as possible, said Richter.

The expert added that while long-term efforts must be placed on helping the world's farmers to grow both rain-fed and irrigated food crops much more efficiently, in mega-cities like Mexico City, which is home to some 20 million people, a quick improvement can be made by repairing the leaks of pipes transporting water to the city.

"A very high percentage of the water taken from rivers and lakes and brought into the cities actually is lost on the way because of leaks on the pipes used to transport the water. Between 10 and 30 percent of all this water is lost during the transportation and Mexico City is on the high end of that," he said, placing the water loss of the Mexican capital at between 30 and 40 percent.