I remember something about that, too, Panic.
As I recall, as soon as the fuel is ignited, that heat would be sufficient to melt the any frozen water. I imagine it would take a little longer to "warm up". In extreme conditions, a small heating coil could be powered by battery to keep the water in its fluid state.
The de-ionized water in the system is completely sealed which means it would only rarely need to be changed, if at all.
But let's wait to get the definitive answer from Harry, thanks for posting that over there, Grajekk.