As the world's population hits seven billon this week, the United Nations is warning that the planet's water resources will come under intense pressure.

Most population growth is in the developing world and "dwindling water supplies is the environmental issue most often raised in developing countries," says the UN Population Fund's State of World Population 2011 report.

And so they should be, argues Lester Brown, an author and founder of the Earth Policy Institute.

Brown points out that agriculture accounts for 70 per cent of the water used every year on the planet. With more mouths to feed, the world's poorest countries will make increasing demands on the resource.

"The demand for drinking water goes up but that's trivial. The demand for water to produce food is the big one. It takes a thousand tons of water to produce one ton of food. So when we look at the water issue it's really a food issue," Brown says.

Countries like China and India are already buying vast tracts of agricultural land in Sudan and Ethiopia, writes Brown in his most recent book, World on the Edge: How to Prevent Environmental and Economic Collapse. And the purchase of agricultural land means the purchase of the water to irrigate that land.

But it isn't just developing countries that need to be worried. Canada is at risk, too. Canada is to fresh water what Saudi Arabia is to oil. Canada has a lot of it. The problem with that analogy is Saudi Arabia knows how much oil they have (but doesn't tell anyone). Canada, on the other hand, has never done a clear accounting of its ground water resource.

"I use the image of groundwater being like people with straws and blindfolds on in a big bathtub. Everybody's sucking the water out of the bathtub and it's fine until the very moment that the last drop of water is gone," explains Maude Barlow, national chairperson of the Council of Canadians.

Canada, though, is in an enviable position. We may not know how much there is but at least there seems to be plenty. Developing countries with growing populations know they are running out.

That's where groups like One Drop come in. It is a non-governmental organization started by Guy Laliberté, the founder of Cirque du Soleil. The group uses theatre to educate people in developing countries — like Haiti — about water. It also partners with Oxfam on projects to bring water to those most in need.

"The issues of water today are issues of poverty and not issues of resources," says Marie-Anne Champoux-Guimond, One Drop's water and education adviser. "We have to change our behaviour and our relationship with water because we don't use it in a sustainable way."