Believe me, it is no big deal to keep your highly rated helmet with your SAR pack. I did it for decades and it is worth the significantly greater overall protection, not just side impacts. I have seen relatively minor incidents involving the head resulting in fatalities and, conversely, one major trauma to the victim's climbing helmet wearing head which he survived. That made me really believe in the value of a UIAA rated climbing helmet. There are lots of ways to gather water.