There are 2 options available for Natural gas being storage or continuous flow sometimes called instantaneous. Continuous flow hot water units heat the water as you use it, making them more costs efficient as they do not heat hundreds of litres of water all day. They also never run out of hot water like storage tanks which are limited to the amount of water they can hold so often the last person can get a cold shower. They are available in natural gas and LPG to suit your gas type.