Ground clearing to start in weeks for the $508 million project after decades of debate.

A controversial, $508 million water treatment plant is now all but certain to be built this spring by the City of Austin after nearly a quarter-century of debate.

A split Austin City Council voted Thursday in favor of the project, targeted for a site near the Oasis restaurant along Lake Travis.

A four-member majority of the council ultimately sided with the argument that Austin needs to build the plant as soon as possible or risk shortages of treated water as early as 2014.

Three dissenting members of the council said the plant would not be needed for years, if ever, and argued that the money could be better spent on water conservation measures, such as fixing city water pipes that leak billions of gallons of water each year.

With Thursday's vote, crews will begin clearing land in the coming weeks.

"It is a gamble not to build the plant now," said Mayor Lee Leffingwell, its chief advocate through the recent debates. "And I will not roll the dice with the health and safety of the people of Austin."

The outcome of Thursday's vote was not a surprise because the swing vote on the issue, Council Member Randi Shade, had said Tuesday that she would be supporting the plant. She and Leffingwell said it would not hinder water conservation efforts.

But some environmental activists came to Thursday's meeting anyway to voice opposition to the project in a spirit activist Paul Robbins described as "our fight in the shade" — a reference to a quip from ancient Spartan king Leonidas, who according to legend, said prior to the Battle of Thermopolae that if the opposing Persian army could blot out the sun with its arrows, "then we will fight in the shade."

"The world has changed since we started down this path" of building the treatment plant, Save Our Springs Alliance executive director Bill Bunch said. "Maybe it's time to start down a different path."

Council Member Bill Spelman, citing years of teaching statistical analysis as a University of Texas professor, said his analysis showed that per capita water use in Austin and across Texas had been declining in a steady line since the 1960s, and that ultimately led him to the conclusion the plant was unnecessary. He said that the expected cost — which will raise water rates 12 percent — amounts to $515 for every man, woman and child in Austin until the bonds are paid back.

Before the meeting, Spelman and his fellow plant critics on the council, Chris Riley and Laura Morrison, called on the city to adopt a more comprehensive water plan and restructure its water rates so that the treatment plant does not raise the bills of low-income families and small businesses. Their resolution is likely to come before the council at its Nov. 5 meeting.