A leak in a beach house often announces itself differently, because so much of the plumbing is where you can see it.
Look underneath first
Before anyone starts talking about detection equipment, walk under the house. Damp patches, green staining on fittings, drips and rust marks on supports are all visible without any tools. On an elevated home that simple look answers the question a surprising amount of the time.
A test you can do in a minute
Turn off every tap and anything using water, including the outdoor shower, then check the meter. If it is still moving, water is going somewhere it should not.
Rentals hide leaks
If a property is only occupied part of the year, a slow leak can run unnoticed for months. Comparing your water bill against the same month last year is one of the more useful things an owner can do here.
Why it matters more on an island
Salt air and constant humidity mean damp timber does not dry out. A slow leak onto framing under a beach house turns into rot faster than the same leak would inland, and that repair is far larger than the plumbing that caused it.