Which type of fire would be most effectively extinguished with water?

Water is most effective for extinguishing Class A fires, which involve ordinary combustibles such as wood, paper, textiles, and some plastics. These materials are solid and can absorb water, allowing it to cool the burning material, remove heat, and suppress the fire. The chemical process that occurs when water is applied effectively interrupts the fire triangle—fuel, heat, and oxygen.

Class B fires, which involve flammable liquids like gasoline and oils, and Class K fires, which pertain to cooking oils and fats, require specialized extinguishing agents that do not use water, as water can spread these flammable liquids and may worsen the situation. Class D fires involve combustible metals (like magnesium or sodium) that react violently with water. Thus, using water on these fires can be extremely dangerous and is not appropriate. Therefore, water's effectiveness in cooling and extinguishing combustible materials makes it the appropriate choice for Class A fires.