Deep space isn't entirely applicable - remember that in a vacuum, the problem isn't generating heat, it's dissipating it. A 'mech would be far more likely to overheat in deep space than it would to freeze.<br/><br/>But yeah, I doubt any mech would be bothered by icy water, considering every one of them is toting around a small fusion reactor as a power source. Just shutting down some or all of the heat sinks would be enough. The bigger danger is a breach of hull integrity once combat starts.