Water-flux rates of eight free-living lions, Panthera leo, were measured using tritiated water. Water-influx rate averaged 49.5± 7.5 ml kg-1day-1. This is only slightly higher than predicted water-influx value in captive animals under standard conditions, but over twice as high as predicted water influx in free-living eutherian carnivores. Factors influencing water-flux rates and estimates of food consumption from independent studies were used to determine dependence on drinking water, a constant supply of which is maintained artificially in the study area. Drinking comprised ca. 40% of the total water influx. Keywords: Panthera, water balance, Namibia.