A more accurate measurement for fluid need is body weight. Weigh yourself before and after exercise. A pound will equal 16 ounces of water. Absorption of fluids are enhanced when very small amounts of sodium and sugar are added to the water, as in commercial sports drinks. A cooler temperature of the water also increases the absorption.
Athletes are often concerned with the loss of electrolytes from sweat.
Those electrolytes include sodium, chloride, magnesium and potassium. These losses are minimal. Magnesium and potassium sweat losses are very low and are should not cause concern as long as intake of fruits and vegetables is adequate. Endurance can be enhanced by eating a well-balanced diet and consuming appropriate amounts of fluids. If you have any questions, call your local military medical treatment facility and ask to speak with a registered dietitian.