Going away for three weeks, what's the best way to handle the water heater and pipes?

Legionella bacteria is the main concern here since it thrives in stagnant water within that 20-50°C (68-122°F) range. For a 20-day trip, draining the entire system is ussually more trouble than it's worth. If you have an older water heater, draining it completley can actualy stir up heavy sediment at the bottom, wich often leads to clogged aerators or damaged valve seats when you try to get things running again.

You are already doing the right thing by killing the power at the breaker and shutting off the main valve. Since you're worried about the water sitting, the best approach is a thorough **flushing routine** once you return. There's no need to leave the water warm; letting it sit at room temperature is fine as long as you don't use it immediately upon your return. When you get back, turn the main water valve back on very slowly to avoid a pressure surge. Go around to every faucet in the house and run both the hot and cold water for at least 10 minutes. Make sure you run the showers and flush all the toilets too. This pushes the stagnant water out of the pipes and replaces it with fresh, chlorinated water from the municipal supply.

Once the lines are flushed, then you can flip the breaker back on for the heater. I usually suggest letting the tank get up to its full operating temperature—ideally around 140°F—for a few hours before anyone takes a shower. That thermal shock will handle any lingering bacteria. It's alot safer and easier than trying to manage a bone-dry system for three weeks.

Does the tank dial need to be cranked up specifically for that first day back? Mine is locked at 120°F for safety, so I'm wondering if I have to mess with the settings just to get rid of the bacteria or if the normal temp handles it.

Also, whould it help to pull the aerators off the sinks before running the water for 10 minutes? I'd hate to have all that sitting water push a bunch of grit into the screens and mess up my flow right when I get home.

Definitely pull those aerators. Even without a full drain, the pressure surge when you flip the main back on can knock loose scale or sediment from the pipe walls. It saves you the headache of cleaning them out later.

One thing people overlook is the fridge water line. Since those are small lines, the water stays stagnant. Toss the first couple batches of ice and run a gallon through the dispenser once you're back. Regarding the 120°F limit, it’s ussually fine for city water. Just be absolutely sure you’ve purged all the air from the hot side faucets before you flip that breaker back on, or you'll burn out an element instantly.