The claim states that a standard universal mathematical formula exists for calculating total body water percentage. The retrieved literature demonstrates the exact opposite: numerous distinct prediction equations are developed, validated, and used for specific demographics, age groups, and clinical populations (such as Cameroonian children, hemodialysis patients, and various adult cohorts). Furthermore, reviews note a lack of universal applicability and emphasize the necessity of population-specific models. Therefore, the claim is definitively refuted by the evidence.