The answer to 'difference between tankless water heater and tank water heater' is that tankless water heaters heat water on-demand, while traditional tank water heaters store heated water in a tank. Tankless heaters are more energy-efficient, take up less space, and provide a continuous supply of hot water. However, they have a higher upfront cost and may require electrical or gas upgrades for installation.
Tank water heaters are generally less expensive to install, but they have higher operating costs due to the energy required to constantly heat and maintain the water in the tank. They also have a limited hot water supply that can be depleted during high-use periods.