Charleston County schools ought to be large enough and functional enough to serve the county’s children.

Charleston County ought to have libraries that are accessible and useful to the public.

And the county ought to have adequate streets, roads and highways so people can get to those schools, libraries and other destinations.

But Charleston County residents are already paying 8.5 percent sales tax on every dollar they spend, and that’s a significant bite out of their budgets — particularly low-income consumers. (The state with the highest combined state and local sales tax is Tennessee, at 9.49 percent.)

So if the Charleston County School Board, Charleston County Council and the Charleston County Library Board want to ask voters in 2014 to approve sales tax hikes, they better have some compelling arguments.

The Charleston County School District officials contend that projected growth in Mount Pleasant, West Ashley and North Charleston will exceed schools’ capacity significantly.

Staff is in very preliminary stages of discussing whether to ask voters to extend a penny sales tax (approved in 2010 for school building projects) past 2016 when it is due to expire.

The county library director has been talking about the need for new buildings for several years, and a half-penny sales tax to make it happen.

And County Council probably wouldn’t have much trouble producing a file full of plans for roads that need to be repaired, widened or built. Early indications are that council will ask for a half-cent sales tax also.

But pity the citizens who have watched their buying power shrink under the existing tax burden.

The school board, County Council and library board face the daunting prospect of having to convince those residents to go to the polls in the next general election to tax themselves more. Likely, they’ll be looking for reasons to vote “no.”

What about the remarkably high salaries of the administrative staff at the Charleston County School District?

What about the library’s often criticized policy of tossing out thousands of books just because they haven’t been read in three years?

What about Charleston County’s initial support for a tax increment financing (TIF) district for a high-end development on Johns Island?

County Council terminated that plan to divert $82 million in tax revenue for roads, expanded fire service and a sewage treatment plant for the project only after extensive opposition from the public.

Should any or all of the entities seek a sales tax hike, they will have to convince the public that they have been good stewards of the tax dollars they already get.

And they will have to be wide open with the public’s business. No back-room strategy meetings. No spinning the numbers or the needs.

Only then can voters make an informed decision about the pending sales tax proposals.