“It’s a dry heat,” we Tucsonans tell our concerned relatives from more temperate climates. What we don’t tell them, of course, is that an oven is a dry heat, too, but folks don’t normally go sticking their heads in them.

The fact remains: Tucson is hot. Really hot. And dry. Tucson gets an average of 12 inches of rainfall per year. For comparison, Massachusetts has gotten more than 70 inches of snow in just the past two weeks. Mobile, Ala., gets 65 inches of rain a year. In Arizona, we bake, and in Alabama, they steam.

But that lack of water combined with an ever-increasing population adds up to a very big problem for the Southwest.

Since 1990, the population of Pima County has grown by almost 300,000 people. According to the Washington Post, recent population analyses estimate that Arizona, California, Colorado and Texas will all gain Congressional seats after the 2020 census. People want to live here.

This growing population creates a fundamental problem for most western states past the 100th meridian: There are more people with less water to share. According to the U.S. drought monitor, most of Arizona, California, Oregon, Nevada, Colorado, Utah and New Mexico have been in drought for most — if not all — of our lifetimes.

In Arizona, we depend heavily on water from the Colorado River, but the Colorado River Basin is shared with six states — New Mexico, Utah, California, Nevada, Wyoming and Colorado — and Mexico. To supplement our growing population, the state came up with the Central Arizona Project, which diverts water from the Colorado River and sends it down to Phoenix and Tucson. The U.S. uses so much of the Colorado River water that, for many years, it was not flowing all the way to the end of the delta in the Sea of Cortez, which makes Mexico none too happy.

Groundwater, water pumped from wells, is how most of Arizona, including Tucson, receive its water. Due to the overuse of streams and rivers, as well as growth in the populations pumping ground water, many rivers that were once community beacons of water and life are now bone dry. The Santa Cruz used to run through Tucson just about 100 years ago; today, it only flows when monsoon season hits. Though population growth and water overuse greatly affect Arizona water tables, the laws are also an issue.

Anyone who took seventh-grade science would know that water flows cyclically. Evapotranspiration leads to condensation in the air, which then leads to precipitation. After precipitation, things get a little more complicated, because precipitation leads to streams and rivers that eventually run into oceans. However, it also recharges aquifers and tributaries that move at a snail’s pace. Yet, only one small Arizona law related to subflow legally acknowledges the connection between groundwater and surface water.

Regents’ professor of law Robert Glennon explained some of these odd scientific understandings embedded in Arizona water law.

“The [water] law was developed in the 19th century when hydrology was at its infancy,” Glennon said.

This leads to one of the biggest problems in water law today: Science has far surpassed the efficacy of the law. Today, we understand how groundwater and surface water are connected, but we did not understand that in the 19th century.

“There was a time in the mid-20th century when the Arizona Supreme Court decided to integrate groundwater and surface water,” Glennon said, “but because of a howl of opposition from farmers, the Arizona Supreme Court reverted back.”

With the way things are going, the CAP will likely see less and less water, especially in drought years. So, how does that affect us here in the Old Pueblo?

“What you’re likely to see over time is a decrease in [water] use by agriculture,” Glennon said. “The water will retire to urban use.”

This is troublesome, since a large portion of the state’s economy depends on agriculture. All in all, 21st-century laws need to be developed to respond to new scientific realities. However, until that can happen, we can all make a difference by conserving our water use. Taking shorter showers and turning the water off while brushing your teeth or shaving may sound like hippie propaganda, but it will help sustain our water tables. Though there isn’t much you can do about changing a law — besides talking to your legislators — you can save the amount of water you use and help keep this oven we call home habitable.

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Maddy Bynes is a junior studying political science and history. Follow her on Twitter.