"The supply of water is going down, and the demand is going up, which makes water more expensive," Rhett Larson said.

Larson, a professor of water law at the ASU Sandra Day O'Connor College of Law, says the city receives about 70% of its overall water supply from the Colorado River, which is an increasingly uncertain source given the negotiations between the states that share it.

Arizona’s shrinking Colorado River supply is putting new pressure on cities like Scottsdale and on water bills.

City leaders and water experts are working to come up with solutions to prevent a water shortage. Last week, the Scottsdale City Council voted to raise water rates by 4.5%.

A crowd turned out for a town hall Wednesday to see what’s being done to prevent a water shortage. Professor of Water Law at Arizona State University, Rhett Larson, joined Mayor Lisa Borowsky at the event.

Scottsdale is not running out of water but it is running out of cheap water. That was the message ASU water law professor Rhett Larson gave to a crow of over 100 at Mayor Lisa Borowsky's town hall meeting at the Granite Reef Senior Center May 27.

There is no sitting out the water shortage, Larson said.

"This is not a drought," he said. "There are no 30 year droughts. Thirty year droughts is a new climate."

For decades, scientists and policymakers have relied largely on streamflow, or the amount of water moving through rivers, to measure water availability. But new research published in Scientific Reports shows that approach captures only part of the system.

“The Colorado River flow at Lees Ferry is often treated as the main indicator of water availability, but it’s really the result of many processes happening across the landscape,” said lead author and ASU research scientist Zhaocheng Wang. “By bringing in satellite observations, we’re able to better account for water stored in snowpack and soils, which improves how we understand and predict the system as a whole.”

Cynthia Campbell, a former top Phoenix Water official, was involved more than a decade ago in setting up an earlier Phoenix-Tucson water sharing program in which Phoenix and other Phoenix-area cities stored some of their CAP supplies in Tucson's more plentiful and much larger CAP recharge basins. In return, Phoenix can pull some of Tucson's CAP supplies off the canal when it needs them.

That was a long-term plan, but today, "We really need this level of flexibility right now," said Campbell, now director of policy innovation at Arizona State University's Arizona Water Innovation Initiative.

In Arizona, roughly 85% of residents live in cities that rely, at least in part, on the river.

Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University, said the trend is hard to ignore.

“We have to think of it as the new normal,” Porter said.

The federal government has been consulting with tribes as it works out this complex negotiation over the future of the river. But, as Arizona State University water expert Sarah Porter tells me, there will be no signature line to sign for the 30 tribes that live near the river whenever the states do reach a deal. 

On the other hand, she says, tribal groups with senior water rights typically do have more influence on their state's overall position as they negotiate deep cuts to the water supply. 

In Arizona, a study in the journal Communications Earth & Environment sites groundwater losses in the Lower Colorado River Basin exceeding the full capacity of Lake Mead by 40%. 

Karem Abdelmohsen and Jay Famiglietti, both of Arizona State University, note annual Lake Mead losses average 1.2 million acre-feet, which ultimately affects water use along the Colorado River in Arizona and California.

Lake Mead could again approach these critically low levels over the next several months and years, according to the Bureau. This would depend on both the climate conditions as well as the response to those conditions, Dave White, director of the Global Institute of Sustainability and Innovation at Arizona State University, told ABC News.

"This is a multi-decade-old drought, and then on top of that multi-decade-old drought are the impacts of climate change, which predominantly translate into higher temperatures, more variable precipitation, and drier soils and higher [water] demand," White said.