It rusted out
you have a leak in your heater core which is attached to your radiator and heats the air inside your car interior
a bad water pump could cause low heat. The heater uses the coolant from the pump to generate heat.
busted raditator , check heater-core . most are found inside up under your dashboard . hope that helps you !
Condensation Or the tank rusted out
Check the heater core your water could be antifreeze leaking from it. Either broken connection where hoses connect or bad core itself located inside dash.
The most likeliest answer to this question would be that your hot water heater is unfortunately rusting or perishing from the inside, no amount of cleaning will help. your only option is to replace the hot water heater.
Older heater with rust build up in the bottom of the tank.
I would suspect the thermostat is stuck in the open position so the water ( and motor ) never reach operating temperature. This is common where hard water ( water with a lot of minerals ) is in people's taps. I would suggest replacing the thermostat and draining out the coolant and replacing it with new antifreeze mixed with distilled water. You could have an inoperative blend air door inside the dash, or the heater core is restricted internally.
If it is a electric water heater, then one of the heating elements are burned out.
Heater hose or heater core.
No...
It is a water heater, not a hot water heater. There would be little point in using a hot water heater. I assume that is your point.