A vertical water heater includes a machine body installed therein with plural quartz heating tubes respectively composed of a quartz external tube having its opposite ends sealed and a quartz internal tube positioned in the quartz external tube. Each quartz internal tube is provided with a remote-infrared-ray heating member in the interior and has one end connected with an electrode terminal. Each quartz external tube has its lower wall bored with plural water intakes 212 and its upper wall bored with vapor vents. The machine body has its bottom provided with a water inlet and a water outlet and its topside bored with an exhaust vent having a pressure release valve assembled thereon. The vertical water heater carries out heat conduction by vapor and by light and heat radiation, impossible to produce water stains and able to economize energy.