Water is absolutely fundamental to life. The human body can survive for upwards of a month without food, but will shutdown in less than 3 days without a steady supply of our planet's most abundant liquid. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. In a survival situation, 4 liters (approximately a gallon) should be your daily goal.
Thirst is not a proper indicator of when you should drink water. Thirst is a sign of dehydration, dehydration that you are trying to avoid. Instead focus on the color and frequency of urination. If your pee is yellow, you should be drinking more water. If your pee is clear or very faintly colored, you can rest assured your water consumption is adequate.
