Most people have never heard of the part inside their water heater that's doing the most to keep it alive. The anode rod quietly corrodes itself away year after year, so the steel tank around it survives — and understanding what it does explains why a small piece of metal decides how long your heater lasts.

You step in warm, and three minutes later, the shower turns cold. Or you're second in line in the morning and get a lukewarm rinse at best. If your water heater used to give you a full tank and now quits early, something inside it has changed. The good part: you can usually find the cause and fix it.

You are standing in the kitchen, the house is quiet, and your water heater lets out a sound like someone microwaving popcorn in the garage. Then it does it again the next morning, a little louder. That popping isn't the tank about to blow, but your water heater is trying to tell you something, and the message is worth reading before it gets expensive.

Plumbing doesn't usually headline the renovation plans, but it plays a starring role behind the scenes—and when overlooked, it can throw quite the wrench into an otherwise smooth upgrade.

Plumbing issues can easily be sidelined during a renovation, but overlooking them can lead to costly and inconvenient problems down the line.