Hydration
Hydration describes the body's water status and the process of maintaining enough water for normal function. Fluid intake is one part of hydration, but the terms are not identical: water also comes from food and metabolism, while urine, sweat, breathing, and stool continually remove it.
There is no single daily volume that fits everyone. Body size, energy intake, climate, altitude, pregnancy or lactation, illness, diet, and physical activity all change intake and losses. Under average conditions and adequate energy intake, the DGE reference table for water lists about 1.47 liters per day from beverages and 0.89 liters from food at ages 19 to under 25, and about 1.41 and 0.86 liters per day, respectively, at ages 25 to under 51. These are population reference values, not a universal drinking prescription. Heat, high energy expenditure, fever, vomiting, or diarrhea can increase needs substantially; some heart or kidney conditions instead require individualized fluid limits.
For ordinary daily life, thirst, access to drinks, meals, and broad urine-color trends can guide practical habits. Urine color is only a rough clue because supplements, foods, medication, and the time of day can change it. A single dark or clear sample does not diagnose dehydration or prove ideal hydration.
Exercise fluid needs are especially variable. Comparing body mass immediately before and after a representative session, while recording drinks and urine, can help estimate net loss and an individual sweat rate. The National Athletic Trainers' Association position statement explains both this method and its limitations. Changes in clothing, food, glycogen, and measurement conditions can distort the estimate, so it is more useful as a repeated practical observation than an exact body-water test.
During a short strength workout in a temperate gym, drinking to thirst and eating normal meals is often sufficient. Longer sessions, high heat, heavy sweating, or repeated training may justify a more deliberate intra-workout strategy, sometimes including electrolytes. More is not always safer: drinking fluid faster than it can be lost can dilute blood sodium and cause exercise-associated hyponatremia. The goal is an individualized middle ground, not forced drinking or a fixed liters-per-hour rule.