Lions normally drink water every day if it is available. When researchers have observed prides of lions in the Serengeti and the nearby Ngorongoro Crater they drank after every meal. Although lions can manage without drinking water when it is scarce.
Lions live in a semi-desert habitat and even in desert. Under these circumstances they are able to obtain sufficient moisture from the body fluids and blood of their prey animals such as for the sand cat.
Within the Kalahari Desert, where lions live, there is no surface water. Fritz Eloff tracked several different lion prides in Kalahari Gemsbok National Park for up to 12 days at a time. He found that some prides drank more frequently than others.
On one occasion he tracked three young male lions and observed that they were without water for nine days during a period of intense heat.
Over this period the three lions killed one bat-eared fox and three porcupines. That was the sum total of their prey animals and clearly, therefore, they were not getting much water from their food or food.
On another occasion a group of four adult females and a six-month-old cub drank on the first and third nights while being observed and then did not drink for seven consecutive days. During this time, they killed an ostrich, to adult gemsbok and two porcupines.
In areas such as the Kalahari and other very dry environments, lions regulate their body temperature and reduce loss of water through evaporation by resting during the hottest part of the day.
Lions appear to be primarily nocturnal but there are no hard and fast rules as to when they are most active. Being nocturnal they will be hunting in cooler climatic conditions. Also, of all the cat species, wild and domestic, lions are the least active.
The lions observed in the Ngorongoro Crater were inactive for about 19 hours per day. The observed lions in Nairobi National Park were similarly inactive as they rested for 20-hour periods and spent three hours moving in hunting and about one hour a day feeding. No doubt this helps to keep down loss of water as more activity generates a greater loss of water and moisture from their bodies.
The information about drinking comes from JP Handby and colleagues in Ecology demography, and behaviour of lions in two contrasting habitats: in Ngorongoro Crater and the Serengeti plains published in 1995. Also, FC Eloff in his Water used by the Kalahari lion published 1973. Also, PC Clarke and HH Berry in their Water flux in free-living lions in the Etosha National Park published in 1992. Also, and finally, M and D Owens in their Kalahari lions break the rules, published in 1984.
The information about inactivity and nocturnal activity comes from GB Schaller in his The Serengeti Lion Published in 1972 and JA Rudnai in their Activity rhythm of a free-Ranging lion population published in 1976.