In case of a fire, before the fireman use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Water usually contains salts and conducts electricity. If the electrical supply is not cut off and firemen come in contact with wet electric switches, electric wires and other electrical appliances, they may get electrocuted. So, the electrical supply is cut off to prevent electrocution of firemen.Concept insight: Ordinary water is a good conductor of electricity.