Tampa Bay Water officials say they want to protect water quality in the Alafia River by changing the river’s classification so it must meet drinking water standards.

That argument, however, rang hollow Thursday for some Hillsborough County commissioners. They see the reclassification as a way for Tampa Bay Water to transfer future river cleanup costs to farmers, phosphate companies and county sewer plants in the watershed.

“This is truly a veiled attempt to really nail us with what could be millions and millions of dollars of costs,” Commissioner Jim Norman said.

Tampa Bay Water, the regional water supplier, has a water intake on the river and is allowed to take 10 percent of the river’s flow when the flow is greater than 80 million gallons a day.

The Alafia is now classified as a class 3 water body, meaning it should be clean enough for fishing and other recreation. Changing the river to a class 1 standard would mean more-stringent limitations on the pollutants in the water. If the amount of any of the pollutants failed to meet the higher standards, the state could make industries that discharge wastes into the river spend money on expensive pollution control equipment.

Jerry Maxwell, Tampa Bay Water general manager, says reclassifying the river would keep new polluters from dumping into the Alafia.

“What you’re doing is building this backstop so you can’t slide back worse than you are,” Maxwell said.

Tampa Bay Water purposely scaled back the section of the river it wants reclassified so as not to affect phosphate mines and the county’s Valrico sewer plant, Maxwell said.

An economic cost-benefit analysis done by Tampa Bay Water showed the reclassification would result in little or no economic costs to agriculture, phosphate mining or developers. On the plus side, water customers would receive a benefit of $337.4 million that Tampa Bay Water wouldn’t have to spend on new treatment systems, the analysis concluded.

That finding was challenged in Hillsborough County’s analysis of the Tampa Bay Water study. The county used the water supplier’s own data to show the river would fall short of meeting class 1 water quality standards for fluoride, a pollutant associated with phosphate mining.

“A number of chemicals not exceeding state standards now under class 3 will exceed under class 1,” said Shahrokh Rouhani, a consultant hired by the county to analyze Tampa Bay Water data.

Mario Cabana, a member of the county water team, said if the Alafia is reclassified, the state Department of Environmental Protection could declare the river “impaired” for fluoride and other chemicals. The DEP would then set limits that would force phosphate plants and other industries to install pollution controls.

Tampa Bay Water officials disagree, saying there’s no way DEP officials would declare the Alafia impaired for fluoride.

“It’s not even on their list,” Maxwell said.

Fluoride is a chemical for which water bodies can be classified as impaired, said Jan Mandrup-Poulsen, DEP administrator for watershed assessment. He said the Alafia does not exceed the current fluoride standard of 10 milligrams per liter. But if the water was reclassified to class 1, the state would have to re-evaluate its status under the tougher 1.5-milligrams-per liter standard.

“If the criterion was to change, yes, we would then change our parameters to test the existing data against the revised threshold,” he said.

Tampa Bay Water general counsel Richard Lotspeich said he disagreed with the county analysis. He and Maxwell still intend to recommend reclassification to the Tampa Bay Water board Monday. The final reclassification decision will be made by DEP Secretary Michael Sole and the state Environmental Regulation Commission.