- The majority of fluid output occurs via the urine, approximately 1500 ml/day (approx 1.59 qt/day) in the normal adult resting state.
- Some fluid is lost through perspiration (part of the body's temperature control mechanism) and as water vapor in expired air. These are termed "insensible fluid losses" as they cannot be easily measured. Some sources say insensible losses account for 500 to 650 ml/day (0.5 to 0.6 qt.) of water in adults, while other sources put the minimum value at 800 ml (0.8 qt.). In children, one calculation used for insensible fluid loss is 400ml/m2 body surface area.
- In addition, an adult loses approximately 100ml/day of fluid through feces.
- For females, an additional 50 ml/day is lost through vaginal secretions.
These outputs are in balance with the input of ~2500 ml/day.