Tank water heaters mostly fail from the inside out — corrosion wins, a seam or fitting lets go, and the tank empties onto the floor while the supply line quietly refills it. That's why a "small leak" can become dozens of gallons overnight. The honest version of what to do next: stop the refill, kill the heat source, dry everything within 24–48 hours, and don't sign anything while the floor is still wet. On bare concrete, this is often a shop-vac-and-fans problem, not a contractor problem.
Tank water heaters typically last 8–12 years. The manufacture date hides in the serial number on the data plate — for many brands the first letter is the month (A=Jan) and the next two digits the year, though formats vary; the Advisor can decode yours from a photo. Why it matters twice: an old heater explains the failure to your insurer as sudden rather than neglected, and if the one that just failed was 12 years old, its twin in the house next door — or the one you're about to buy used — is on the same clock. Past ten years, the honest advice is to plan replacement on your schedule rather than the tank's.
Water reached finished rooms, drywall, or carpet; it ran for hours unnoticed (came home to it, or it's in a closet inside living space); a ceiling below is wet; or things still read damp after two days.
Water stayed in the utility area but touched the drywall base or stored items. Dry hard, watch for musty smells or stains over the next week, and test only if a question remains.
Bare concrete, caught the same day, dried within 48 hours. Replace the heater, keep the area ventilated, and you very likely don't need to spend anything on the water side.
The pattern insurers apply: sudden failure, resulting damage covered; the heater itself, usually not; slow neglected drip, often denied. A tank that let go is normally the first kind — which is why the dated photos and the serial-number shot matter. If the heater sits in living space and water reached flooring or walls, document extra carefully before anything is removed. Your insurer makes the call, not us — call them early. Fair-price context for any repairs they don't cover is in our cost guide.
Three honest, cheap moves: a drain pan plumbed to a drain under any heater inside living space; a leak sensor on the floor beside it (they cost less than a pizza and scream early — we're putting together reviews-and-reputation picks now); and a calendar note at the heater's 10th birthday to price replacement before it's an emergency. If your heater is in an attic or closet above finished rooms, these three go from smart to essential.
Mold can begin on damp materials within about 24–48 hours. Concrete is forgiving; drywall, carpet, and stored cardboard are not. Dry hard for two days and move porous items out of the wet zone.
On bare concrete, dried within two days — usually no. Water into drywall, carpet, finished rooms, or a ceiling below, or a leak that ran unnoticed for hours — get an honest read promptly. Acting fast is almost always cheaper than the mold that follows.
Sudden failures are commonly covered for resulting damage (not the heater); slow neglected leaks often are not. Photograph everything including the data plate, note the age, and call your insurer early.
Get an honest read before you spend anything. The AI Mold Advisor will tell you if this is a dry-it-yourself situation — on concrete, it usually is.
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