Which term describes a dehydration condition primarily caused by the loss of water?

The term that best describes a dehydration condition primarily caused by the loss of water is hypertonic. In a hypertonic situation, the solute concentration outside of the cells is higher than that within the cells, which leads to water moving out of the cells in an attempt to balance the concentration gradient. This movement of water out of the cells can lead to cellular dehydration, where the cells lose water and shrink.

In contrast, isotonic refers to a state where the solute concentrations are equal on both sides of the cell membrane, maintaining a balanced fluid environment. Hypotonic indicates a lower concentration of solutes outside the cell compared to the inside, causing water to move into the cells and potentially leading to swelling or bursting. Fluid balance generally refers to the overall homeostasis of fluids in the body rather than a specific condition of dehydration or excess. Thus, hypertonic is the most accurate term to describe the condition identified in the question.