How can tankless water heaters heat water instantly?

When you open the faucet of your shower, the flow of the still cold water triggers the heater to turn on. Then the powerful gas burners or electrical elements will turn on, rapidly heating the water as it passes through the vessel. The water is heated instantly, and the time it takes to obtain hot water mainly depends on the distance the hot water has to travel from the water heater to your shower. The burners or elements shut down as soon as you turn off the faucet. You only have to pay for the energy that you used to heat the water for taking this shower.