Old World rat species of the kind commonly found in cities need to drink water daily, while Dromedary and Bactrian camels can go without water for weeks. However, kangaroo rats, which are not closely related to Old World rats, can live their entire lives without drinking a drop of water.
One particular species of Old World rat is actually known as the water rat because it often lives near water sources to meet its hydration needs. Kangaroo rats and camels are all desert species, and they have evolved effective means of dealing with arid conditions. Kangaroo rats are able to reuse water from metabolism, and they only drink when absolutely necessary, explains the Animal Diversity Web. Both groups of animals are very efficient at retaining water, but camels do need to drink more frequently.