What is it called when an individual consumes too little water?

The condition characterized by an individual's consumption of too little water is known as dehydration. Dehydration occurs when the body loses more fluids than it takes in, leading to an insufficient amount of water necessary for normal physiological functioning. This can result in various symptoms, including thirst, dry mouth, fatigue, and more severe health issues if not addressed.

In contrast, the other terms refer to different concepts. Hypervolemic pertains to an excess of fluid in the body, whereas hypovolemic refers to a state of decreased blood volume, which is often a result of significant fluid loss, including dehydration. Hypotonic describes a solution with a lower concentration of solutes compared to another solution, typically referring to osmotic pressure and not fluid intake. Thus, the most accurate term for consuming too little water is indeed dehydration.