These hot water systems use an electric element to heat the water. In general, the water is always kept at a specific temperature, so you are paying to keep the water in the tank hot all the time, even when you are not using it. Usually, electric storage hot water heaters are the cheapest option, they are also the most popular option.
As its name suggests, this is a gas hot water system (natural gas or LPG) that only heats the water when you turn on the tap, saving you money by not storing heated water continuously in a tank.
These are an environmentally friendly option that operate like your refrigerator but in reverse. Instead of creating a cold environment like a refrigerator, heat pumps create hot water using electricity to transfer heat from the air into the water. They are more energy-efficient than electric hot water systems and so help to reduce your hot water bills.