How to tell if i'm dehydrated? and what to do to fix it?

Thirsty? Dark urine?: If you are thirsty, you are already about 5% volume depleted. If your urine color is dark yellow toward brown shades, you are very concentrated, consistent with dehydration. Drink water at about 1 qt/hr max, with occasional electrolyte containing drink if dry from exertion. If thirst resolves / urine lightens, then you have improved your situation. If not, see dr for advice & assistance.