What types of fire can plain water be used on?

Plain water can effectively be used on Class A fires, which involve ordinary combustibles such as wood, paper, and cloth. It can also be utilized on some Class B fires, specifically those involving flammable liquids, if the fire is small and manageable. However, water should never be used on Class C fires (electrical) or Class K fires (cooking oils and fats), as it can exacerbate the situation or pose safety risks. Always assess the fire type before applying water.