We did the same trip this past Jan. The only place we found to fill up with water was, like sail445 said, in Culebra at the Dingy Dock bar. We filled up the two 30 gallon jerry cans we had from a spigot and shuttled them back to the boat via our dingy. Made 3 trips. This is a two person job as hauling the cans from dingy to boat is heavy work.