Because the pipework under an elevated house is out in the open, water line problems here are usually easier to find and easier to fix than on the mainland.
Exposed pipe has advantages
No breaking up slabs, no opening walls to trace a leak. If a supply line under the house is weeping, we can usually see it, get to it and repair it the same visit. That is one thing about beach house plumbing that genuinely works in your favour.
Insulation and heat tape
The trade-off is exposure to cold. Pipe insulation degrades in sunshine and salt air, and heat tape has a finite life and needs to actually be plugged in and working. Both are worth checking every autumn rather than assuming what was fitted years ago is still doing its job.
Pipe supports rust through
Metal hangers holding pipe under the house corrode in salt air, and once one fails the pipe sags and strains its joints. It is a small, cheap thing to replace and a genuine cause of leaks if left.
The line from the street
If pressure has dropped throughout the house rather than at one tap, the service line may be the problem. On small island lots that is usually a short run, which keeps a replacement straightforward.