I think the point is that water is a universal need - whether you're in the sahara or the arctic, you're going to need water. Warmth is only necessary in certain situations, not as "important", for some ill-defined meaning of "important".
Well, proper temperature should be regulated either direction for optimum health. Too cold, you get hypothermia, too hot & you get heat stroke. Either extreme can quickly kill you faster than dehydration. Eh, maybe they worded it poorly...
