Water is the universal solvent and the medium through which all known cellular biochemistry occurs. Life depends on water to maintain cell structure, transport nutrients, and allow complex metabolic processes to function. Organisms surviving in environments with little or no liquid water have evolved specialized strategies to manage this fundamental need. These methods range from complete biological shutdown during desiccation to highly efficient internal water generation and conservation. Understanding these adaptations reveals the remarkable flexibility of life to sustain itself under conditions that would be lethal to most species.
Survival by Cellular Shutdown (Anhydrobiosis)
The most literal answer to what can live without water is a group of organisms capable of entering anhydrobiosis, or “life without water.” These creatures endure the complete desiccation of their bodies, losing nearly all internal water content, yet remain viable for years or even decades. This process effectively halts metabolism and prevents the cellular damage that would normally occur when water is removed.
A key mechanism involves the production of protective molecules, such as the sugar trehalose, common in organisms like brine shrimp and rotifers. Trehalose acts as a water replacement, forming a glassy, amorphous matrix that stabilizes cellular membranes and proteins. This glass-like state, called vitrification, physically prevents sensitive biological structures from collapsing or denaturing as water evaporates.
The mechanism used by the microscopic tardigrade, or water bear, is more complex and species-dependent. While some tardigrades utilize trehalose, others rely on specialized proteins known as tardigrade-specific intrinsically disordered proteins (TDPs). These TDPs are highly abundant and also form a protective vitrified matrix upon drying. By inducing this state of cryptobiosis, these organisms can survive extreme conditions, including the vacuum of space, until water returns and metabolism reactivates.
Water Sourcing Through Metabolism and Conservation
Other animals survive in arid environments by becoming masters of water conservation and internal sourcing, rather than completely drying out. These organisms still require water for life processes but avoid the need to drink from external sources. They achieve this through a combination of physiological and behavioral adaptations that maximize water gain and minimize loss.
Desert mammals, such as the North American kangaroo rat, derive almost all their necessary hydration from metabolic water. This water is a byproduct of oxidizing energy-containing substances like fats and carbohydrates found in their diet of dry seeds. For example, every hundred grams of fat can yield over 100 grams of water when metabolized.
Water loss is further minimized through highly efficient kidneys, which produce the most concentrated urine of any mammal. This allows them to excrete waste with minimal water expenditure. Desert rodents are also nocturnal, avoiding the hottest part of the day by sheltering in cool, humid burrows. Some species recapture moisture from their breath through specialized nasal passages that condense water vapor before it is exhaled.
Specialized Plant Storage and Retention Mechanisms
Plants in arid regions, known as xerophytes, employ structural and physiological adaptations to survive prolonged drought. These mechanisms focus on either storing large volumes of water or drastically reducing the rate of water loss to the atmosphere. This strategy differs from anhydrobiosis because the plant’s metabolism remains active, although at a reduced pace.
Cacti and other succulents, like aloes, are the most prominent examples of water storage, a process called succulence. They possess specialized, fleshy tissues in their stems or leaves that swell to store water absorbed during infrequent rain events. The root systems of these plants are often shallow and widespread, designed to rapidly absorb surface moisture before it evaporates.
Water retention is achieved through structural modifications that drastically limit transpiration. Many xerophytes have reduced their leaves to spines, which minimizes the surface area exposed to the sun and wind. A thick, waxy layer called a cuticle also covers the plant’s surface, acting as a sealant to prevent uncontrolled water evaporation. These adaptations allow the plants to maintain turgor by drawing upon internal reserves during extended periods of drought.