Drinking

Drinking is the process of ingesting water or other liquids into a body. This can happen through a mouth, a proboscis, or other parts of an organism.

For humans, drinking is essential to maintain tissue hydration. Water is required for many different physiological processes to function correctly. If a person does not take in enough water, they may suffer from dehydration. Conversely, drinking too much water can lead to water intoxication. This condition occurs when the concentration of salts in the body becomes dangerously diluted.

In humans, the mechanics of swallowing involve a specific sequence of events. When liquid enters the mouth, the swallowing process is completed by peristalsis. Peristalsis is a series of movements in the esophagus that delivers liquid to the stomach. Gravity also assists in this movement.

Humans use various methods to ingest these liquids. We might pour liquid from our hands or use drinkware as vessels. We can also drink by sipping or sucking, which is common when using a spoon or consuming hot liquids. Infants use a suction method by pressing their lips tight around a source. This creates a vacuum using a combination of breath and tongue movement.

Animals in the wild use many different motions to drink. Most free-roaming animals stay hydrated by eating foods with high moisture content.

When they must drink from bodies of water, their methods vary by species. Canines, such as dogs, lap water by scooping it into their mouths. They use their tongues in a shape similar to a ladle. Cats drink differently because their tongues are smooth. Only the tip of a cat's tongue touches the water. The cat pulls the tongue back quickly to create a column of liquid. This liquid is then secured when the cat closes its mouth.

Other land mammals use different physical actions to reach water. Ruminants and many other herbivores partially submerge the tip of their mouths. They use a plunging action with their tongues held straight.

In the savanna, giraffes have a unique method that may defy gravity. Scientists have theorized that their long necks might function like a plunger pump. Elephants have a unique way of drinking as well. They draw water into their trunks and then squirt it into their mouths. Some animals in frozen environments, like tree squirrels or bighorn sheep, eat snow or icicles to get moisture.

Insects and birds also have specialized ways to manage hydration. Many insects obtain water from their food, but they can drink from standing water if they are dehydrated.

Some terrestrial insects constantly absorb humidity from the air through their cuticles. The desert insect *Onymacris unguicularis* has even evolved to drink from nighttime fog. Birds typically scoop water into the buccal areas of their bills. They then raise and tilt their heads back to swallow. The common pigeon is an exception, as it can suck in water through inhalation.

Aquatic life manages water intake through different biological systems. Amphibians and freshwater animals do not need to drink through a mouth. Instead, they absorb water steadily through their skin by osmosis.

Saltwater fish face a different challenge and must drink through their mouths as they swim. They must also purge excess salt from their bodies through their gills. These fish drink plenty of water and excrete a small volume of concentrated urine to manage their internal balance.

Human water requirements are influenced by many environmental factors. The USDA recommends a daily intake of 3.7 liters for adult males and 2.7 liters for adult females. These figures include water found in other beverages and foods. However, experts note that actual needs depend on activity level, body size, and sweat rate. The hypothalamus in the brain regulates thirst by responding to changes in blood volume and electrolyte levels. A persistent and extreme desire to drink is a psychological condition called polydipsia. This can sometimes be a symptom of diabetes mellitus or diabetes insipidus.