Fluids are gained through drinking, eating, IVs, and feeding tubes. The kidneys eliminate about 1-2L of urine per day on average, calculated as 1mL per kg of body weight per hour. Sweating through the skin can lose up to 1000mL per hour depending on temperature, while continuous insensible perspiration loses around 600mL of water per day. The lungs eliminate about 400mL of water vapor per day, and the GI tract loses 100-200mL on average despite circulating 8L per day.

1. ROUTES OF GAINS AND LOSSES
 water and electrolytes are gained in variuos ways. A healthy person gains fluids by
drinking and eating. Fluids may be provided by the parenteral route (IV or subcu)
or by means of an enteral feeding tube in the stomach or intestine.
KIDNEYS
 the usual daily volume in the adult is 1L to 2L . a general rule is that the output is
approximately 1mL of urine per kilogram of body weight/hour in all age group.
SKIN
 sensible perspiration refers to visible water and electrolyte loss through the skin
(sweating). The chief solutes in sweat are sodium chloride and potassium. Actual
sweat losses can vary from 0 to 1000mL or more every hour, depending on the
enviromental temp.
 Continuous water loss by evaporation (6oo mL/day) occurs through the skin as
insensible perspiration, a nonvisible form of water loss. Fever greatly increases
insensible water loss through the lungs and the skin, as does of the natural skin
barrier.
LUNGS
 The lungs normally eliminate water vapor (insensible loss) at a rate of 400 mL
every day. The loss is much greater with increased rate depth, or in a dry climate.
GASTROINTESTINAL TRACT
 the usual loss through the gastrointestinal (GI) tract is only 100 to 200 mL daily,
even though 8L of fluid circulates through the GI system every 24 hours (called the
GI circulation). Because the bulk of fluid is normally re-absorbed in the small
intestine and fistulas cause large losses. In healthy people, the daily average
intake and output of water are equal.