This is a picture of a water heater I have seen in several locations in the world. It is an electric heater and heats the water as you use it. When they work as they are supposed to they work very, very well. I would even be amenable to using one at home. However, you can’t just use one. Everywhere that you need hot water, you need one of these. At least, I assume so. I’m not sure what would happen if you only had one and someone was taking a shower, a load of clothes was washing and the dishwasher was going. Then again, a thoughtful person wouldn’t do that, would they?