Final answer:
Water extinguishes fire primarily by reduction of temperature, absorbing heat and thereby lowering the temperature of the fuel below its ignition point. This is especially challenging in the case of oil fires, where crude oil's lower density than water can complicate the extinguishing process.
Step-by-step explanation:
The principle which most closely describes how water extinguishes fire is reduction of temperature. When water is applied to fire, it absorbs heat as it raises in temperature, transitions from liquid to gas during boiling, and as the resulting steam's temperature continues to rise. This absorption of heat reduces the temperature of the burning material to below its ignition temperature, effectively putting out the fire. This process is crucial, especially in challenging situations like extinguishing a fire on a crude oil tanker, where a large amount of energy is released from the burning oil. Furthermore, the fact that crude oil is less dense than water introduces additional complications as the water might not adequately cover the burning oil surface to extinguish the fire.