The simplest ones are of two styles. The first uses a simple impeller wheel much like a net pump on a well, sucking water from a reservoir and flinging it out into the room. This produces cold "steam". The second method uses two carbon rods dipped into the water reservoir and connected to the mains. The water heats and releases hot steam into the room. The water has to be somewhat conductive for this to work (contrary to common belief, pure distilled water is an insulator) so a small amount of table salt is sometimes added to the reservoir if enough set a m is not being produced.