By Max Deveson
BBC News, Washington
The arid states of America's south-west have been getting drier in recent years.
Since 2000, the Colorado River - which provides water for seven US states in the region - has carried less water than at any time in recorded history.
And while the drought is worsening, the demand for water in this booming part of the country is increasing.
The states dependent on the Colorado River for their water are seeking solutions to their water shortage, with some suggesting that importing water from far-flung states - or even towing icebergs down from the Arctic - could solve the problems.
Meanwhile, the US states and Canadian provinces of the water-rich Great Lakes basin have drawn up an agreement to restrict the export of water from their region.
How availability, use and needs are changing across the world
Experts say this pattern - of water shortages in dry regions, and protective agreements in wet areas - is likely to repeat itself elsewhere as the world demand for water begins to exceed supply.
The seven US states served by the Colorado River commissioned a study in 2006 to look into ways to augment their existing supply of water.
"The water levels that we considered normal flow just aren't going to exist anymore," said Pat Mulroy, chief executive of the Southern Nevada Water Authority.
The states asked consultants to consider the feasibility of 12 potential options, ranging from the large-scale re-use of household wastewater, to the importation of fresh water from further afield.
Importing water is not a new idea. For years, engineers and politicians have been coming up with proposals to transport water from water-rich northern California or Alaska down to the desert south-west.
In the early 1970s, the US Bureau of Reclamation began looking into the idea of building an underwater aqueduct to carry water from northern California to the south of the state.
The feasibility studies were never completed, but in the 1990s, Alaska Governor Walter Hickel resurrected the idea of an ocean pipeline, this time to transport water from Alaska to the south-west US.
Again, however, the plans were discarded.
The consultants acting for the seven Colorado River states also looked into the pipeline option, and concluded that such a project could potentially bring large quantities of water to the region.
The plan would pose serious technical difficulties, cost billions of dollars, and could threaten Alaska's fish population.
They also looked in to the possibility of shipping water down from the north-west, either in refitted oil tankers or specially-designed nylon bags that could be towed by tugboats.
Several companies have been formed in recent years promising to make water transportation a reality, according to the consultants' report.
One such firm - Transglobal Trade - has signed long-term agreements with Native American groups in Alaska for bulk water rights, although it has yet to begin shipping it.
And Global H20 Resources, a Canadian firm, has been granted rights to 4.8bn gallons of glacier water every year for 30 years by the Alaskan city of Sitka.
For years, engineers have dreamed of tapping into the freshwater resources of the Arctic, by towing icebergs from northern waters down to California.
But such proposals have always foundered because of the impracticability of insulating the ice to prevent melting in transit.
Although the Colorado River states did consider some of these ambitious water importation schemes, their engineers concluded that projects closer to home - like water conservation, and desalination of ocean water - were more practical and realistic options.
"I would describe some of the [water importation] options as 'brainstorming'," said Southern Nevada Water Authority spokesman Scott Huntley.
"But that doesn't mean that one day water importation from further afield couldn't become a reality."
"The Colorado river system will ultimately have to be augmented from somewhere," added Pat Mulroy.
"But it's more feasible to divert floodwaters from the mid-west than to get water from Canada," she added.
'Awash in water'
During last year's presidential election campaign, one candidate for the Democratic Party nomination - New Mexico Governor Bill Richardson - called for a National Water Policy, noting that Great Lakes states like Wisconsin were "awash in water".
No official suggestions have been made for large-scale transfers of water from the Great Lakes basin to the parched south-west.
Chicago diverts 2bn gallons of water daily from the Great Lakes
But that has not prevented the US states and two Canadian provinces that surround the lakes to draw up an agreement restricting the export of water from the region.
The agreement - known as the Great Lakes-St Lawrence River Basin Water Resources Compact - bans any new diversion of water from the Great Lakes basin, though "limited exceptions could be allowed in communities near the Basin when rigorous standards are met".
It is these "limited exceptions" that worry the Council of Canadians, which campaigns for sustainable water usage in Canada, and whose chairperson Maude Barlow advises the UN General Assembly's President on water issues.
The Council warns that by granting special rights to communities and counties straddling the Great Lakes, the compact will allow "vast amounts of water [to] be transferred outside the Great Lakes basin, which will have adverse effects on its ecological integrity and lead to further depletion of water in the basin".
"The Great Lakes are in trouble," Ms Barlow said. "People say there's plenty of water here - but that's what they said about the Aral Sea in Russia."
Chicago already diverts 2bn gallons (7.5bn litres) of water every day from the Great Lakes basin, and the compact does little to prevent the city taking even more water.
Bottled water companies are also exempt from the agreement, which the Council says could lead to the unacceptable exploitation of Great Lakes.
"Once bottled water corporations are granted this right it will be difficult to regulate taking water out of the Great Lakes in containers because the practice would be protected in international trade agreements such as the North American Free Trade Agreement (Nafta)," it warns.
The council fears that if water is designated as a commodity under Nafta, a precedent would be set, and large-scale export of Canadian water to the US would become legally unstoppable.
"I doubt that the south-western US states will be looking to the Great Lakes for their water - but they may well look to parts of northern Canada," said Ms Barlow.
US President Barack Obama has emphasised the need to conserve water and notably did not include any big water projects in the stimulus package.
This suggests that the incoming administration will not look kindly on any grand schemes to bring water to the parched south-west.
Pat Mulroy agrees with this analysis.
"There has to be a mosaic of solutions - but conservation and re-use should be at the forefront of any strategy", she told me.
The lesson may well be that to keep the water flowing in the desert, it makes little sense to tow icebergs down from the Arctic, or to divert water from the Great Lakes.
But water there is should be conserved, re-used and treasured as the precious natural resource that it is.