Folly Beach is on treated municipal water, so this is something we recommend selectively rather than as a matter of course.
You are not on well water here
It is worth saying plainly, because coastal living makes people assume the water needs treating. It does not. The supply is municipal and treated, and the salt in the air has nothing to do with what comes out of your taps.
What people actually notice
Chlorine taste is the usual complaint, and a filter at the kitchen tap handles it for a fraction of the cost of a whole-house system. In a rental, a simple drinking filter is a small touch guests appreciate.
Where sediment filtration helps
In older cottages with ageing pipework, a sediment filter protects taps and appliances from the debris coming off the inside of those pipes. That is a modest and sensible bit of equipment.
Ask for a test first
Anyone recommending a large system for a Folly Beach address without testing your water is working from a price list rather than from your house.