While a human requires a minimum of 125 oz (3.7 liters) of water to maintain vital signs, your actual needs to just maintain basic survival are much higher. Read the Article in Water Myths and read the Hydration Articles. According to the USA EPA an average family uses nearly 400 gallons of water each day which puts it at an average of 100 gallons per day per person. In an on grid situation 27% of the that 100 gallons is expended flushing toilets.
Whether you are hiking, camping, or just hunkered down in your home during a hurricane the best approach to maintaining your optimum healthy hydration you should limit your salt intake to between 3 and 5 grams, you should eat a lot of water-containing foods (fruit, vegetables) and drink water in moderate amounts throughout the entire day. But it is not water alone that you need you require a delicate balance of minerals, electrolytes and essential fatty acids in order to absorb the water into your blood and cells.
Let's get real though, you just got rousted from your domicile you are excited, high heart rate, high stress, heavy lifting, carrying, exertion beyond most people's monthly activity level in one day, you are going to burn off, sweat off and use way more than these minimums. That’s why you should understand hydration and how to spot the early signs of dehydration.