I  like the hot water heater idea, but caution all considering it and
planning on using it on their drinking water supply - current automotive
coolants are extremely toxic. So much so that accompanying cautions warn
not to leave it uncovered during a coolant change, as pets may drink it
and die. So if  a leak develops in your water supply, it could be
hazardous if you are also using that supply for drinking and cooking.

Although a copper tube is very unlikely to develop a leak, a separate
supply of drinking water might help your peace of mind.

DDF