Water jet extinguishers operate by spraying a jet of water at the burning objects, cooling them and stopping them from re-igniting. They are not to be used on live electrical devices.
Water spray extinguishers use a very fine spray of water droplets, each surrounded by non-conductive air. Any water spray fire extinguishers have a 35 kV dielectric test permit, which ensures they have been measured at one metre on a 35,000 Volt electrical source.
Water extinguishers with additives are extinguishers that have foaming chemicals added to them. The water loses its normal surface friction, allowing it to soak more effectively into the burning materials. Since the additives are mixed into the water, a smaller extinguisher will achieve the same fire rating as a bigger, water-only extinguisher.
Water mist or fog extinguishers apply water in the form of mist or fog, with even smaller droplets than a water spray extinguisher. The bigger the droplet, the greater its surface area in comparison to its size, the faster it evaporates, absorbing heat energy. The disadvantage is that the heavier the droplet, the less it weighs and therefore the less strong the water cloud.