Thirst is first

Thirst is a warning that you are already dehydrated

Dark yellow-orange urine is another sign Urine should be a clear, light color unless

You’ve been taking medicine or eating foods that add color

Dry mouth and headache mean stop and drink soon

Dizziness and weakness indicate impending heat exhaustion – a serious problem

Dehydration also invites muscle cramps (especially the thin muscles on your back)

In cold conditions, dehydration greatly increases the likelihood of frostbite

You lose water quickly when you’re sweaty and working hard, even in cold weather

Less obvious is that you dehydrate drastically just standing still at high altitude or in any dry cold, let alone when exerting yourself That has been a factor in many mountain –climbing disasters