Over the coming month, Atlanta voters will be cajoled with radio ads, posters in MARTA stations and speeches by the current and former mayors of the city -- all aimed at getting them to renew a 1 percent sales tax to pay for water and sewer projects.

The tax could raise between $400 million and $440 million by 2016, according to the city's estimates. The city says funds generated by the tax would keep rates from rising higher than necessary.

On March 6, the day of Georgia's presidential primary, city voters will be asked to renew the "municipal option sales tax," which has raised more than $700 million for the city since October 2004. Much of that cash has paid for upgrades required by consent decrees with state and federal regulators, such as better pipes and treatment plants.

Those requirements came after decades of neglect led to serious sewage spills around Atlanta.

The law prevents city officials from advocating for a vote one way or the other. But in interviews and pamphlets, they are adamant about what they see as the consequences of a "no" vote: water and sewer rates rising by 25 percent to 30 percent over four years, as well as more infrastructure problems if maintenance is deferred.

Without the tax, "we would have to raise the rates to meet our bond covenants," Mayor Kasim Reed told The Atlanta Journal-Constitution. "That is just a fact."

Atlanta voters have already approved the tax twice -- about 75 percent of voters backed it in 2004, and 71 percent supported it in 2008.

Atlanta has completed about two-thirds of the work required to meet a 2014 regulatory deadline. The remaining work could cost $480 million.

The tax spreads the burden of paying for big sewer projects to hundreds of thousands of commuters and tourists who visit Atlanta every day but do not pay its water bills, Reed said.

Atlanta's water and sewer rates already combine as the most expensive in the country, the result of eight rate increases stretching back to 2004. The latest rate hike, a 12 percent increase, came in July.

The Department of Watershed Management estimates that it will spend about $40,000 on an educational campaign about the tax.

Without the tax, the department would have to plug a $113.1 million fiscal hole, or about a fifth of its budget, said Jo Ann Macrina, the department's commissioner. A series of 5 percent rate increases in each of the next four years would be the most likely strategy if the tax expires Sept. 30, she said. Rate increases would require approval from the City Council.

The sewer tax vote will be on the same ballot as Republican presidential candidates in what promises to be a hotly contested primary.

Some Republicans are anti-tax across the board, said Brad Carver, vice chairman of the Fulton County Republican Party. But there is room for debate about this particular measure, he said.

"I hate to say ‘good' in front of the word ‘tax' at any time, but I do agree that consumption taxes are a better way to go," he said. "They are broadly based, and they're more fair [than income taxes]."

In addition, "we have to do these types of infrastructure projects" to recruit companies and jobs, Carver said.

John Sherman, president of the Fulton County Taxpayers Foundation, said he is skeptical about the efficiency of the Department of Watershed Management. Based on an audit several years ago, he said, “there is a need for an independent oversight by a group of professional engineers.”

But Sherman also said he thinks the tax is necessary. “Otherwise,” he said, “the water fees would explode.”

Atlanta's 8 percent sales tax is already among the highest combined rates in the nation, and its combined water and sewer bills are the highest for average users.

Former mayors including Shirley Franklin, Sam Massell and Andrew Young have made themselves available to advocate for the tax in grass-roots meetings over the next four weeks.

"It's really a must-do -- it's not really optional," Massell, now president of the Buckhead Coalition, said of the tax. "On the one hand, you have the federal government mandating what we must do. That's not a bad thing, but then you have to come up with ways to pay for it."