GLOSSARY

Fluid Retention Index names a retention metric, not necessarily the beverage hydration index unless its formula and interval match.

Retention describes how much ingested fluid remains over the observation period, not merely how much was swallowed. Urine, other losses, beverage composition and food affect it. A retention percentage needs a defined denominator and time interval. Greater retention in a short experiment does not automatically mean better health or performance, and may be undesirable in someone with fluid overload.

The beverage hydration index compares cumulative urine after water with cumulative urine after a test drink over the same protocol interval. A higher ratio generally reflects lower urine output than water under those conditions. Resting tests do not rank overall health or competition performance. Interpretation needs the observation time, dose, starting hydration and study population rather than simply choosing the highest number.

The kidneys regulate water and solute excretion to stabilize the internal environment, alongside thirst and vasopressin signaling. They do not create new water. Exercise, illness and some medicines can alter these responses. Fluid swallowed is therefore not identical to fluid retained, and increased urine after substantial drinking can represent normal regulation rather than proof that water cannot hydrate the body.

After a session, assess drinks and meals against time until the next workout; urine losses continue, so swallowed volume is not assumed to equal restored volume.

Fluid balance is the difference between input and output over a stated interval. Positive or negative values need a starting context: positive balance may restore an earlier deficit, but sustained excess is not inherently beneficial. Define the interval, intake, urine and estimated losses consistently. Otherwise two apparently different balance values may simply reflect different recording methods rather than physiological change.

After exercise, remaining deficit, time until the next session and continuing losses shape recovery. Meals and their sodium contribute, so restoration need not come from one large bottle. Short recovery windows warrant more deliberate planning, but rapidly forcing intolerable volumes to restore a scale reading is inappropriate. Distributing intake with food can be more practical than treating recovery as a single drinking event.

Water comes from more than plain drinking water: milk, tea, other beverages, fruit, soup and moist foods contribute. Total water intake therefore differs from beverage volume alone. Sugary drinks also supply energy that should match fueling needs. A product's water content by itself does not establish it as the best choice for every training situation or justify unnecessary calories.