Survival skills
A human being can survive an average of three to five days without the intake of water. The issues presented by the need for water dictate that unnecessary water loss by perspiration be avoided in survival situations. The need for water increases with exercise.
Water intoxication
Water intoxication can be prevented if a person's intake of water does not grossly exceed their losses. Healthy kidneys are able to excrete approximately 800 millilitres to 1 litre of fluid water (0.84 - 1.04 quarts) per hour. However, stress (from prolonged physical exertion), as well as disease states, can greatly reduce this amount.