The finding is prompting lawmakers to explore water restrictions that could limit the amount of new lawn and force contractors and property owners to install drought-tolerant landscaping.

The state is expected to add 11 million new residents by 2030, and at least half are expected to locate in hotter, inland areas where homes with lush lawns are popular.

“Do the math,’’ said study co-author Ellen Hanak, an economist in San Francisco. “We’re facing the prospect of many more people with more lawns and gardens in the states hottest, driest regions. That adds up to a lot of water.”

Landscaping currently accounts for at least half of all residential water demand, the report says.

Without new conservation efforts, the amount of water going to outdoor landscaping is predicted to rise by 1.2 million acre feet a year — enough to serve roughly 4.8 million people. California cities and suburbs currently use about 9 million acre-feet of water a year.

Assemblyman John Laird, D-Santa Cruz, is pushing legislation to implement recommendations from a state-sponsored landscape task force. The group’s January report offered 43 recommendations it said could save enough water to serve 2 million households.

One recommendation Laird embraced was to require landscape water meters for new developments where the size of the landscaped area is 5,000 square-feet or greater.

Hanak’s report concludes that given the state’s historic love affair with lawns, land-use patterns influence water demand more than climate in future demand projections.

It shows that future shortages could be exacerbated by the dominance of single-family homes on relatively large lots in the state’s fast growing interior — particularly the greater Sacramento region, the San Joaquin Valley and the Inland Empire in Southern California—where much of the future projected growth is expected.

The hotter inland climates can force homeowners to use two to three times more water than owners in coastal areas, Hanak’s report states.

Bob Drobny, manager of Zamora Sod Farm in Chico, which sells sod from Yuba City to the Oregon border, said his company has been doing strong business as the inland population has boomed.

“You almost can’t buy a house that isn’t landscaped in the front and back with grass being an integral part of it,’’ Drobny said.

The report does not suggest that people get rid of lawns altogether, simply that they get rid of grass where they do not need it, for example front yards.

Even with people who are concerned about the environment, however, that could be a tough sell.

Joseph Nykodym, a Walnut Creek attorney, installed an automatic watering system 10 years ago and makes his own compost because he cares about the environment.

But Nykodym still has a 400 square-foot front lawn, as well as a backyard lawn. He likes the lawn for the most obvious reasons, “it’s nice and it’s soft.”