FORT WORTH — At the plant that treats most of the city’s sewage, water sloshes and foams within giant concrete walls. This is cleaned-up sewage, made even purer by processes the plant expanded just a few months ago. Now, some treated water runs through specially labeled, purple-colored pipes to irrigate nearby golf courses and a park, instead of just getting dumped into the nearby Trinity River, as has happened for decades.

With Texas facing dramatic population growth and constraints on its water supplies, interest in the use of sewage — “reclaimed water,” in industry parlance — is growing. The current 10-month drought, which the state climatologist has called the third worst in recorded Texas history, has prompted a flurry of calls to Fort Worth’s plant asking for reclaimed water, which is cheaper than potable water.

“We can’t provide it fast enough,” said Jerry Pressley, a water systems superintendent at the plant. The plant has provided reclaimed water for about a decade to one golf course next door, but it recently expanded its facilities and is upgrading its technology so that soon the wastewater headed for golf courses will be further disinfected via ultraviolet light rather than with chlorine, which can be toxic in large concentrations.

Like Fort Worth, cities across the state are providing a growing amount of their sewage to parks or golf courses, which use it to water their grounds. But more ambitious projects are planned. In Big Spring, a Permian Basin city that gets relatively little rain even in wet years, a local water authority plans to break ground within the next few months on a $13 million treatment plant that will send about 2 million gallons per day of well-cleansed sewage, called “raw water,” back into the regular water system that serves Big Spring, Snyder, Odessa and Midland.

The Big Spring plant, which will take sewage that has already gone through a wastewater treatment plant and treat it further before blending it into a pipeline with lake water, should be operational by late 2012, said John Grant, general manager of the Colorado River Municipal Water District, which is building it. It appears to be the first plant of this kind in the state,and one of few if any in the country that are taking such a direct approach to sewage reuse.

“It fits our needs and our situation out here,” Grant said, noting that planning had begun well before the current drought, which threatens to dry up the last of the water district’s three reservoirs by December 2012.

The state has a number of projects that send treated sewage water back into major water systems, albeit somewhat less directly. One of the newer ones is in the Tarrant Regional Water District, which serves Fort Worth, Arlington and a few other cities. The project, in operation since 2009, sends some water from the Trinity River (which is highly polluted, due partly to discharges from wastewater-producing plants, including Fort Worth’s) through a specially constructed wetland area and into a reservoir, where it will be reused in the water system. That project is set to expand over the coming decade.

In El Paso, a project that began working in 1985 pumps treated wastewater into the aquifer, where it will eventually be pumped up again for use.

Texas has emerged as a national leader in reuse projects, along with Florida, California and Arizona, said Ellen McDonald, a Fort Worth-based water resources engineer with Alan Plummer Associates, an environmental engineering firm that has helped design a number of projects. Texas, she added, may even be ahead of the other states in “indirect reuse” projects like that of the Tarrant Regional Water District (which her firm helped design) that filter water through wetlands before sending it back into the system. Of course, all discharged sewage ultimately goes back into the global water system, although even more indirectly.

The Texas Water Development Board, the state’s water planning agency, projects that by 2060, 14 percent of the state’s new water supplies, or 1.6 million acre-feet of water, will come from reused water. That’s about double the amount reused today, which (in addition to irrigation) goes toward purposes like power-plant cooling water and outdoor fountains. The water development board expects water reuse projects to be particularly concentrated in the greater Dallas-Fort Worth metropolitan area, which has a large population that will need substantial new resources and has found it tough to build new reservoirs.

Texas has used reclaimed water for more than a century, according to a February report from the water development board. Its earliest uses were for agriculture, when treated sewage was spread on fields near cities like San Antonio and Amarillo. Use of reclaimed water for industrial purposes, like refineries, began in the 1940s, and cities like El Paso, the driest big city in Texas, began using reclaimed water for golf courses and other irrigation purposes in the 1960s.

Past droughts have spurred renewed interest in water reuse projects, and the current one may be no exception. “It’s a good time for public education on the importance of water and other sources,” McDonald said. But she cautioned that the projects can be very expensive and can take awhile to plan and get approved.

For users of reclaimed water, the product brings several benefits. In Arlington, where the Chester W. Ditto Golf Course has been watering about 90 acres with reclaimed water from Fort Worth’s water treatment plant for the past few months, each unit of water costs about 40 percent less than conventional potable water, said Brick Scott, the course’s superintendent.

The lower price “allows me to put more on the golf course,” said Scott, who estimated that he ultimately has shaved about 20 percent off the course water bill. (The drought means that irrigated areas need more water to maintain greenery.)

Because it uses reclaimed water, the golf course is also exempt from drought-related watering restrictions in Arlington, although because North Texas has been hit less severely by the drought than the rest of the state, none are in effect yet. (A year-round ban on watering during the heat of the day is in effect for everyone, regardless of the type of water used.)

Signs around the golf course indicate that the irrigation comes from nonpotable water, and “it’s been a blessing this year,” Scott said.