Water extinguishers are fire safety devices designed to combat Class A fires, which involve ordinary combustible materials like wood, paper, and textiles. They work by cooling the burning material and removing heat, effectively extinguishing the flames. These extinguishers are filled with water and are typically marked with a red label. Water extinguishers should not be used on fires involving flammable liquids, gases, or electrical equipment, as they can worsen the situation. They are easy to use and are often found in homes, offices, and public buildings, making them a common choice for fire safety.