Properly maintained, a traditional water heater can last anywhere between 8 and 15 years, and tankless water heaters tend to have even longer lifespans. However, you will know it is time to invest in a new model if you notice any of the following signs: water takes a long time to heat, or doesn’t heat up properly at all, rust-colored water, water with a strange smell, or water pooling at the base of the water heater.