Water heaters rarely fail without warning. Rusty or discolored hot water, rumbling or popping noises from sediment build-up, water pooling at the base, and a sudden drop in hot-water supply are the classic red flags.
If your unit is over 10 years old and showing any of these, plan a replacement before it fails on the coldest night of the year. A proactive swap is far cheaper than emergency water-damage cleanup.