A little warning for the creative DIY cheap water-heater builders. Beware of the risk of legionnaires disease. Expecially systems where the water stays in the system for several days (like when used 1000 liter cubes or 100m irregation pipe in the system) are at risk.

Also it is not a good idea to connect this type of water heating system directly to the cold water supply. The bacteria will grow in the heated up pipes and can contaminate the cold water supply if there is a direct connection. If you use water without chlorine (like from a well) the risk is even higher. Don't kill yourself out here.

Mark