
Water is the most essential nutrient. You can survive weeks without food but only days without water.
Functions of water in the body:
How much do you need?
Signs of dehydration: Dark urine, fatigue, headache, poor concentration, constipation.
Myth busted: "8 glasses a day" has no scientific basis. Individual needs vary significantly.
Reference:
TaskLoco™ — The Sticky Note GOAT