LAS VEGAS (KLAS) — Southern Nevada residents are laser-focused on Lake Mead as worries over water supplies grow. And rightfully so — that’s the source of almost all of the Las Vegas valley’s water.

But as Lake Mead shrinks even more over the next two years, a reality will come clearly into focus: There’s more demand for the water flowing out of Hoover Dam than there is for the water that stays in Lake Mead.

Water supplies for California and Arizona are pulled out of the Colorado River as it flows out of Lake Havasu. Both states have rights to amounts of water that dwarf Nevada’s allocation.

Biggest users

Under the Colorado River Compact, California gets 4.4 million acre-feet from the river. Drought restrictions that just went into place cut Arizona’s allocation to 2.2 million acre-feet — a 21% cut from the 2.8 million acre-feet under the terms of the compact. Nevada gets 275,000 acre-feet this year — a reduction of 25,000 acre-feet because of the drought.

In this Thursday, Oct. 15, 2015 photo, mechanic John Harper walks onto the pipes conveying water pumped from the Colorado River at the Metropolitan Water District of Southern California’s Whitsett Intake Pumping Plant near Parker Dam, Calif. The pumping plant is the starting point of the Colorado River Aqueduct. (AP Photo/Jae C. Hong)

Here’s how it gets to the states that hold the largest shares of Colorado River water:

CALIFORNIA AQUEDUCT: At Parker Dam, about 155 miles south of Hoover Dam, California’s supply is diverted into the Colorado River Aqueduct. From there, a 242-mile system of pipes, pumps, tunnels, reservoirs and open canals transport the water to where it is used. The water supplies metro Los Angeles and San Diego.

ALL-AMERICAN CANAL: A separate canal delivers water from the Imperial Dam, about 30 miles northeast of Yuma, Arizona, to California’s Imperial Valley, an important agricultural area. The All-American Canal — 82 miles long — irrigates 630,000 acres of farmland and supplies water to nine cities. A branch called the Coachella Canal carries water north.

CENTRAL ARIZONA PROJECT: Arizona’s supply leaves Lake Havasu near the Bill Williams National Wildlife Refuge, extending 336 miles into central and southern Arizona — the system known as the Central Arizona Project, built between 1973 and 1993.

To feed these massive delivery systems, water flows out of Lake Mead through Hoover Dam, Lake Mohave and Davis Dam, eventually reaching Lake Havasu.

The combined storage capacity of Lake Mohave (1.8 million acre-feet) and Lake Havasu (646,000 acre-feet) is just 37% of the water that goes to California and Arizona each year. The U.S. Bureau of Reclamation said Thursday in a report that it would keep the two lakes at their current levels while Lake Mead shrinks. But even if Mohave and Havasu were drained completely, that wouldn’t be nearly enough water to meet the states’ allocations for a single year.

Evaporation losses

An analysis by the Southern Nevada Water Authority (SNWA) recently cast new attention on how much of the Colorado River is lost each year to evaporation — an estimated 10%. And that has been a flashpoint in the relationship between states in the Colorado River Basin.

Upper Basin states have objected to Lower Basin states’ failure to account for water waste due to evaporation. Colorado, Utah, Wyoming and New Mexico have factored in evaporation and “transit loss” — seepage in canals — for a long time.

The canals in California and Arizona are criticized as a wasteful delivery system. A proposal to save 2 million acre-feet of water suggests subtracting those losses from each state’s water allocation. The framework of the proposal was put together by two Nevada agencies: SNWA and the Colorado River Commission of Nevada.

“It is well past time to prohibit the inefficient delivery, application, or use of water within all sectors and by all users,” the proposal says. “There simply is no water in the Colorado River System left to waste and each industrial, municipal, and agricultural user should be held to the highest industry standards in handling, using, and disposing of water.”

“This is something the federal government must do right now,” Andy Mueller, director of the Colorado River District, told Arizona Public Media in September. “They have the right to do it under the (Colorado River) Compact. They have the right to do it lawfully. They just don’t want to do it because it hurts and it’s maybe going to bring in litigation.”