About one-third of global food production depends on non-renewable ground water.
That is not sustainable, said Peter Gleick of the Pacific Institute in Oakland, California, during the Water in a World of Seven Billion conference in Calgary May 9-12.
“We are going to have to figure out how to move to sustainable food production with renewable water resources, and that is a problem when we are running into peak constraints on non-renewable water,” he said.
Fossil ground water is non-renewable. It is found in California’s Central Valley, the Ogallala Aquifer of the U.S. Great Plains, Libya, the north China plains and central India.
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The Ogallala serves a large food producing area, and policy makers are encouraging farmers to switch from irrigation to relying on precipitation as ground water levels are drawn down.
Water can be renewed, but no more is available for the season once it has all been withdrawn from a river or lake. This is known as peak renewable water. The concept has encouraged users to reduce withdrawals without losing productivity in agriculture, power generation, industry and municipal use.
Withdrawals have slowed in the last 30 years, although the human population continues to swell. The practice of water productivity, where more is done with less, has gained traction.
“In the United States today, we use less water in total than we used in 1980 on a per capita basis,” Gleick said.
If water withdrawal had continued at the rate scientists predicted 30 years ago, the United States would have required an additional 800 cubic kilometres to satisfy its current demand.
“I don’t know where we would have found it in the United States.”
Water productivity is sometimes associated with economics rather than conservation.
For example, the American steel industry used 200 tons of water to make a ton of steel in the 1930s, which had fallen to 20 to 30 tons by the 1980s.
By 2002, an efficient manufacturer required two to three tons of water to produce a ton of steel.
This was the result of new waste water discharge and treatment standards that were introduced in the 1980s. It was cheaper for the steel industry to generate less waste water.
Farmers are also figuring out how to grow more food with less water because it cuts input costs.
Nevertheless new sources of water are needed.
Building a new dam or pumping another aquifer was once the answer to match demand with traditional sources of supply.
If it ran out, water was transferred from elsewhere.
Finding new sources of water requires creativity.
Some jurisdictions in southern California treat waste water to high standards and return it to recharge ground water or restore inflow needs for local streams. It also provides surface water for industrial processes.
Other jurisdictions are building large underground cisterns to capture excess rainfall for landscaping and flushing toilets.
Climate change and its impact on water supply must be considered along with environmental degradation.
The problem is that no one fully understands the risks to humans from ecosystem degradation. Total global water withdrawals are not well known to project future demand. Groundwater reserves are also not well known.
“We don’t know where we are in terms of water use. We don’t know how much the world has and we do not know the key components of the hydrologic cycle or the world’s water balance,” said Gleick.
“We don’t know how much ecosystems need for minimum maintenance.”
Water conservation and research must continue.
“There are human, ecological and environmental costs to doing nothing.”
The human impact on the environment has far reaching effects on the water cycle.
“As our use of water starts to grow as we use more and more, the economic value we get out of that water starts to grow, but the ecological value starts to drop,” Gleick said.
More water may be withdrawn for industrial purposes, but the fish may start to die as stream flows drop or pollution increases.
“There comes a point where the next unit of water we use causes more harm than it provides benefit, and the total value starts to go down.”
Gleick said it is time to design modern water management policies, clarify institutional roles and update water laws around the world. Some legislation is 100 years old and was written when needs were different.
