Mark Twain famously said that, in California, water flows uphill toward money. But political machinations, such as the water grab that enabled the metropolis of Los Angeles to sprout in a land of little rain, aren't uniquely Californian.

Today the epic water rights battles fought in the arid West - over irrigation, drinking water, ecosystems and dams - are moving east, as a growing population and changing climate put new pressures on water availability.

In 2007, a Southeast drought provoked a fierce court battle over the waters of Lake Lanier. The combatants were Georgia, Florida and Alabama - states that used to have plenty of water. In the Great Lakes region, falling lake levels led to the Great Lakes Compact of 2008 that outlawed most water transfers out of the eight-state region.

By 2013, 36 states expect water shortages, according to the U.S. Government Accountability Office, likely sparking many more contentious legal battles over this vital resource. It's better that we begin planning today for the shortages to come, rather than waiting for the courts to decide.

To begin, we need to realistically evaluate the population capacity of regions based upon local water availability. Our ancestors settled near life-giving sources of water. We may think we've engineered our way out of that necessity, but our quick fixes - dams and long-distance pipelines - are risky solutions in that they encourage unsustainable population levels. The Great Lakes Compact serves as a better model; it keeps water local, providing for the region's current and future population.

Also, we shouldn't estimate a region's carrying capacity with old, bad data. Otherwise states could end up with something like the 1922 compact that divided the Colorado River among seven western states. Planners calculated the river's hydrology using data from the previous 20 years, which were abnormally wet. To make matters worse, each state was awarded a specific volume of water, not a percentage of total annual flow. Cities like Las Vegas and Phoenix have boomed on the back of this and other water deals. Today, regional water managers are scrambling to find yet more water to meet the needs of growing Western populations, even as climate change is making existing water resources more erratic.

Unfortunately, this type of mistake is being repeated across the country as water managers place huge bets on an uncertain resource, our groundwater. Groundwater is the source of half of Americans' drinking water and 40 percent of our crop irrigation. With demand rising, no one knows with certainty how long uncharted aquifers will last.

"The concept of 'peak water' is very analogous to peak oil. ... We're using (up) fossil groundwater," writes Peter Gleick, an internationally recognized water expert. "That is, we're pumping groundwater faster than nature naturally recharges it."

We know that many aquifers are being depleted, but at what rate is unknown. That's because we lack national data on how much groundwater we have, how rapidly we're extracting it and how quickly it replenishes itself. The federal government needs to collect national aquifer data now. The U.S. Geological Survey has begun studies, but it lacks sufficient funding.

Another hurdle to accurately assessing availability is that many states have laws that regulate surface and ground water differently. But because the two systems are linked, this can result in over-allocation of water and shortages. The Great Lakes states, Nevada and Utah are among those that have created uniform treatment of ground and surface water withdrawals; the rest should follow suit.

Finally, we must banish a holdover from 20th-century thinking that any freshwater that reaches the ocean is "wasted." That concept handily served our interests - or so we thought. But unless policy makers reserve water for ecosystems, human extraction of water will destroy the terrestrial, freshwater and coastal ecosystems vital for human survival.

In 2009, national media personalities hyped as ludicrous California's decision to retain water in the Sacramento Delta to protect an unassuming fish, the delta smelt, rather than divert it to farmers. But the delta smelt is part of the food chain upon which salmon depend, and delta waters are critical to preserving the salmon fishery. Are farms more important than commercial fisheries? Draining ecosystems of water not only devastates water-based economies, it also weakens natural flood control, causes soil loss and water pollution, inhibits groundwater recharge and reduces recreation opportunities.

In the 21st century, water may still run uphill toward money, but we need to quickly learn that we can't sell more than we have.

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Erica Gies is a freelance reporter whose work has been published by the New York Times, the International Herald Tribune, Wired News, Grist, and E/The Environmental Magazine. She lives in San Francisco.