CARSON CITY, Nev. — In Sin City, one thing that will soon become unforgivable is useless grass.

A new Nevada law will outlaw about 31% of the grass in the Las Vegas area in an effort to conserve water amid a drought that’s drying up the region’s primary water source: the Colorado River.

Other cities and states around the country have enacted temporary bans on lawns that must be watered, but legislation signed last week by Gov. Steve Sisolak makes Nevada the first in the nation to enact a permanent ban on certain categories of grass.

Sisolak said that anyone flying into Las Vegas viewing the “bathtub rings” that delineate how high Lake Mead’s water levels used to be can see that conservation is needed.

“It’s incumbent upon us for the next generation to be more conscious of conservation and our natural resources — water being particularly important,” he said.

The ban targets what the Southern Nevada Water Authority calls “non-functional turf.”

It applies to grass that virtually no one uses at office parks, in street medians and at entrances to housing developments. It excludes single-family homes, parks and golf courses.

Nevada Assemblyman Howard Watts III, the bill’s sponsor, said he hopes other western states consider similar action leading up to 2026, when they renegotiate the Colorado River’s Drought Contingency Plan.

He applauded Sisolak for taking concrete action on conservation after Utah Gov. Spencer Cox asked people to pray for rain last week.

“There’s broad acceptance in southern Nevada that if we can take some grass out to preserve the water supply for our communities, then that’s something that we need to do,” he said.

The measure will require the replacement of about 6 square miles of grass in the metro Las Vegas area.

By ripping it out, water officials estimate the region can conserve 10% of its total available Colorado River water supply and save about 11 gallons per person per day in a region with a population of about 2.3 million.

“Replacing non-functional turf from Southern Nevada will allow for more sustainable and efficient use of resources, build resiliency to climate change, and help ensure the community’s current and future water needs continue to be met,” said Southern Nevada Water Authority General Manager John Entsminger.

The ban was passed by state lawmakers with bipartisan support and backing from groups like Great Basin Water Network conservation group and the Southern Nevada Homebuilders’ Association, which wants to free up water to allow for projected growth and future construction.

When the ban takes effect in 2027, it will apply only to Southern Nevada Water Authority jurisdiction, which encompasses Las Vegas and its surrounding areas and relies on the Colorado River for 90% of its water supply.