Most CPAP's will tolerate tap water for short periods, usually requiring a descaling more frequently.  The one thing I would recommend if using the ship's tap water for a CPAP is to let the water sit in an open container for several hours before using it in the machine.  This allows the residual chlorine to dissipate (which normally happens when tap water sits in the pipes leading to your house for hours/days) and I would not recommend breathing chlorine vapors.   Also, if you get frie