Most water heaters have a life span of ten to fifteen years.
After that, they should be replaced. If you don't know your tank's age, it's probably time for a new one if it isn't heating as well as in the past, or if rust is visible at the bottom rim of the tank. Sometimes tanks leak prematurely because sludge accumulates too quickly in the bottom of the tank and promotes rusting. Sludge or debris is an unavoidable byproduct of the water-heating process. It can be minimized by having all the water drained out of the tank once a year.