Water heaters are among the more straightforward repair-or-replace decisions, because the failure modes are well understood and one of them is decisive.
The decisive symptom
If water is coming from the tank body itself rather than from a fitting, valve or connection, replace it. Internal corrosion has breached the tank, and that does not get better. Continuing to run it risks a full failure that empties the tank onto whatever is below.
Water from a fitting, valve or pipe connection is a different matter and is often a straightforward repair.
Age as the main variable
Conventional tank water heaters typically last 8 to 12 years. Within that:
Under about eight years. Repair is usually worthwhile. Thermostats, elements, valves and connections are all serviceable components, and the tank probably has years left.
Eight to ten years. The judgement zone. A minor repair may be reasonable; a significant one probably is not, because you may be paying substantially to extend something that is close to end of life anyway.
Over ten years. Replacement generally makes more sense. Even a successful repair leaves you with an aging tank, and the next failure may be the one that empties it.
The Washington hard-water factor
Water hardness varies considerably across the state, and it matters more east of the Cascades. Spokane, Yakima and the Tri-Cities generally have harder water than most of Western Washington.
Hard water leaves scale inside the tank and on heating elements, which reduces efficiency and shortens service life. A water heater in a hard-water area may reach end of life earlier than the general range suggests, and if you are on your second premature failure, water treatment is worth considering alongside the replacement.
Where it sits matters
A water heater in an unfinished garage or basement that fails causes inconvenience. One in a finished space, an upstairs closet or above living space causes damage.
Location should push the decision toward earlier replacement. If failure means water across a finished floor or through a ceiling, the cost of being wrong is much higher, and waiting for a definitive symptom is a poor strategy.
The Snohomish County pattern
Worth noting for growth-era housing. Homes built across the county’s expansion installed their original units at roughly the same time, so a large cohort has been reaching the 8 to 12 year window together.
If neighbours are replacing theirs, that is genuinely predictive rather than coincidental. Planning a replacement is considerably better than reacting to a failure, particularly if the unit sits somewhere a leak would do damage.
While you are deciding
Know where the shut-off is, and check the area around the base periodically. Rust at the base, water staining, or a unit that has started making different noises are all worth acting on before they become definitive.