Fluid imbalance can occur quickly in older adults and in others who cannot express thirst or are in a setting where fluid status is not closely monitored. In tube-fed individuals receiving inadequate calories, severe malnutrition may occur in weeks to months, but improper water intake may lead to critical fluid imbalances in a matter of days. Simplistic equations frequently used to determine fluid needs in adults include milliliters per kilogram of body weight and milliliters per energy (kilocalories) consumed or per energy (kilocalories) need and variations of the Holliday-Segar formula. None of these fluid-requirement equations have been validated through evidenced-based science, and research investigations have revealed that they can grossly overestimate or underestimate fluid needs in the older adult. Clinicians need guidance to better estimate initial fluid needs for the older adult receiving tube feedings and to provide proper close monitoring afterward to avert preventable fluid imbalance-related hospital readmissions, morbidities, and mortalities in this patient population. © 2021 American Society for Parenteral and Enteral Nutrition.