In a newborn infant, water makes up approximately what percentage of body mass, according to OpenStax Anatomy and Physiology?

1. Body water content changes across the lifespan as the proportion of muscle, fat and bone changes. 2. Infants have the highest body water fraction of any age group. 3. Infant body water is about 75 percent of body mass, falling to 50-60 percent in adults and as low as 45 percent in old age. 4. So 75 percent is the correct figure for infants. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 26 "Fluid, Electrolyte, and Acid-Base Balance", p.1248 §Body Water Content_