Has the FreeStyle Libre system been tested in (a) water and (b) sea water?
a. The FreeStyle Libre system was tested to IP27 standards and can be used while swimming, up to 1 meter for up to 30 minutes.1
b. The FreeStyle Libre system has not tested in seawater. There is no reason to expect performance in seawater would be different from fresh water as the salinity would not affect the ability of water to get in to the Sensor.
Reference
1. FreeStyle Libre flash glucose monitoring system User's Manual.