Charleston County Council is about to get down to the business of deciding how to start spending $2.1 billion raised by the half-cent sales tax voters narrowly approved in 2016. Look for the usual 526 suspects to pounce yet again in their never-ending campaign to build The Highway of Their Dreams.

But spend $300 million or more of the half-cent money on 526 and you can’t spend it on something else — like, say, flood relief, Mayor Tecklenburg’s No. 1 priority. Tecklenburg doesn’t have a seat on County Council, but make no mistake: He — and the city — count.

“There is no question the mayor’s voice is critical in this decision,’’ says County Councilman Dickie Schweers. “Always has been, always will be.’’

The city estimates it will cost $2 billion to check the flooding that every year grows worse. That is a huge number for a city with an annual operating budget of about $180 million, with half of that spent on cops and firefighters.

The $2.1 billion the half-cent tax will raise over 25 years is the biggest — and most obvious — source of funding for countywide flood relief. Then there is the $420 million in money the State Infrastructure Bank has earmarked for 526 if Charleston County can come up with the $300 million (and growing) needed to complete the project.

Let County Councilman Brantley Moody and others raid the half-cent money to go with the SIB money to build 526 and you have, with a single vote, exhausted the two largest sources of money that could be used for drainage and flooding. We can’t keep building roads from one place that floods to another place that floods.

Three devastating floods in 23 months have awakened us from our long collective slumber. Mayor Tecklenburg acknowledged as much when he spoke in January to a packed house at Gage Hall convened by Groundswell!, a downtown neighborhood group focused on flooding.

When he ran for office, Tecklenburg said his top three issues were traffic, education and housing. Now, two years later, he listed his priorities in this order: drainage and flooding, traffic and housing. In his State of the City address last month, he said flooding was his No. 1 priority. He didn’t even mention 526.

Tecklenburg wouldn’t be the first politician to tell his constituents what they want to hear. Talk is cheap. Saving Charleston is not. Crunch time will come over the half-cent money.

“If the county will approve the half-cent that would be terrific,’’ Tecklenburg told me. “I’d say we can use the money from where ever we could get it.’’

The ordinance County Council passed authorizing the half-cent vote and the ballot itself make clear that money can be spent on drainage. The money can be used for the following projects:

“For financing the costs of highways, roads, streets, bridges, and other transportation-related projects facilities, and drainage facilities related thereto,’’ the ballot question reads. That language is repeated three times in the document.

Review the tape from the July 2016 council meeting when the ballot question was debated and you will see Councilman Teddie Pryor specifically insisting that drainage be included as eligible for funding. He was assured it would be.

The mayor needs to speak up for his No. 1 priority, which is allegedly flooding, not 526. Tecklenburg says he remains committed to 526 “in the long term,’’ but governing is all about making hard choices.

Despite his new commitment to flooding, Tecklenburg and the city have adopted a minimalist approach to new funding. City Council in December raised water bills $2 a month, and the mayor is pushing a state bill that would make it easier to use local tourism taxes on flooding. Every little bit helps, but it creates no new revenue, only allows the same pie to be divided differently.

If the mayor is serious about making flooding his top priority, he and City Council should pass a resolution asking County Council to designate a big portion of the half-cent money for drainage and flooding. The giant $200 million West Calhoun drainage project is next up for the city, and it would be a good place to start spending the money.

It makes for a good sound bite to say we have to do both, complete 526 and save the city from the rising tides. But how can we do both when we have shown a complete inability to do even one? Fix flooding first.

Steve Bailey writes regularly for the Commentary page. He can be reached at sjbailey1060@yahoo.com.