I never use hot water, copper lines and sediment build up in the hot water tanks could wipe out a tank full of fish in a heartbeat.
I use straight tap from the outside faucet and it runs through a carbon bottle, during the colder months(probably not feasible for most) I just run the return a bit slower and the fish get use to it long enough to survive till the heaters get to it. I've drop temps as far as 10degs without a problem.
For those that are running larger tanks and are north I would probably get an inline heater and do it that way.