Water is critical for the function and survival of snakes, snake tissue is 65 to 80 percent water. Snakes obtain water through diet, metabolic function, and the environment. Only a small percentage of water mass is obtained from ingesting food and breaking it down so most snakes depend on access to fresh water. Snakes drink mostly from ponds, streams, lakes, and waterfalls, but they also drink droplets that form on their bodies, leaves, and rocks.
Advanced snake species seal their jaws to suck water into their mouth cavity and by utilizing buccal pumping (periodically compressing the mouth cavity) water is forced into the esophagus. Some species of snakes are able to drink without sealing the margins of their jaws. Additionally, the mouth cavity contains mucosal folds which trap and attract water through capillaries. This allows snakes to move water towards the esophagus through squeezing the mucosal folds. The urge to drink is driven by the loss of water mass.
Snakes contain a pair of simple kidneys whose function is to filter blood and remove waste products. The concentration and volume of urine are proportional to the water intake of the snake. An overhydrated snake will produce diluted urine with great volume, while a dehydrated snake will produce a small volume of concentrated urine. Urinary waste is carried from the kidneys to the cloaca where further water absorption can occur. The breakdown of protein by proteases produces a nitrogenous waste called uric acid, the salts of uric acid are called urates. Thus water is lost in excreted waste. Internal biological mechanisms also rely on water as an input, depleting the supply.
Water is also lost through cutaneous evaporation, that is off the skin of the snake. Within the stratum corneum section of the epidermis lipid bodies are secreted from α-cells which fill the spaces between alternating layers of keratin forming lamellar bilayer sheet which functions as a permeability barrier. In desert snake species the α-cells secrete a high quantity of lipid bodies called lamellar granules, this lowers the rate of evaporation. In contrast to desert species, snakes living in moist environments have a much lower quantity of lipid bodies allowing for bidirectional movement of water. During ecdysis (shedding) some species have the ability to adjust this permeability barrier in response to environmental changes.