Which of the following statements regarding fluid requirements for healthy adults age 18-55 is correct?

• A. They require 25 ml/kg/day.
• B. They require 35 ml/kg/day.
• C. They require 15 ml/kg/day.
• D. They require 45 ml/kg/day.

Answer: (B)

Fluid needs for healthy adults are often estimated with a weight-based rule. For adults aged 18–55, about 35 mL of water per kilogram of body weight per day is a practical, evidence-based starting point. This amount helps cover obligatory losses from urine and stool, plus insensible losses through skin and respiration, and it scales with body size so larger individuals need more fluid each day. It also provides a comfortable margin to account for day-to-day variations in intake and activity. For example, a person weighing 60 kg would aim for roughly 2.1 liters per day, while someone at 70 kg would aim for about 2.5 liters. Of course, factors like exercise, fever, hot environments, or certain medical conditions can raise or lower needs, but 35 mL/kg/day is the standard target for healthy adults in this age range.