Do these three things first
If water is pooling under your water heater, deal with safety and the water supply before you work out why.
- Stay out of water near electricity. If the puddle has reached an outlet, extension cord, power strip or any wiring, don’t step into it and don’t touch anything plugged in. The CDC says to turn off the power at the main breaker when electrical circuits or equipment are wet or near water, but only from a dry spot. If you would have to stand in water to reach the panel, call an electrician.
- Shut the heater down. For an electric heater, switch off its breaker at the panel, and don’t touch the wiring or the access covers on the tank if they’re wet. For a gas heater, turn the gas control on the tank to off, following the instructions on its label. If you smell gas, leave the house and call your gas utility from outside. The water may be hot, so keep children and pets away.
- Close the cold water supply to the heater. The City of Phoenix tells residents leaving home for a long time to shut off the water to the heater “where it enters the heater.” That valve sits on the cold-water pipe that feeds the tank. Turn it by hand. The Smart Home Water Guide, from the City of Phoenix and other Valley water providers, warns that old or corroded valves can break. If it won’t close, use the main shut-off for the house. Our shut-off valve guide shows where that usually is.
Closing the supply stops new water from entering the tank, but a leaking tank can keep seeping what’s inside. Put down towels or a shallow pan and move stored boxes away.
Then take photos and video of the heater, the puddle and everything wet. Arizona’s Department of Insurance and Financial Institutions advises taking pictures before any plumber or restoration contractor shows up.
Find where the water is coming from
“Leaking from the bottom” doesn’t always mean the bottom of the tank has failed. Dry the tank and floor, lay down paper towels, then use a flashlight to follow the wet path upward.
The relief valve and its pipe
Every tank has a temperature and pressure relief valve, usually called the T&P valve, with a discharge pipe running down from it. The valve is there to release water if the temperature or pressure inside the tank gets too high. If water is dripping from the valve or out of that pipe, the valve has opened or is leaking. That points to the valve or the pressure, not a hole in the tank. A plumber can find out which.
The drain valve
Near the base of the tank is the drain valve, used to flush out sediment. It can drip if it wasn’t closed all the way after draining, or if it has worn out. A drip from the valve is a valve problem, and the tank may still be sound.
Fittings dripping down from above
The cold-water inlet and hot-water outlet usually connect at the upper end of the tank. A slow leak at one of those joints can run down the side of the heater and collect at its base, where it looks like a bottom leak. ENERGY STAR lists leaks from joints, seals or seams among its signs that a heater may need replacing.
Condensation and other nearby sources
Cold-water pipes can sweat on humid days, and the drops can land near the heater. Condensation usually leaves a damp film or a few drops. A puddle that keeps coming back after you dry it is more likely a leak.
Check what else is close by. A water softener, a washing machine or an air conditioner’s condensate line may be the real source. For AC drains, see our guide to an AC leaking water through the ceiling.
The tank itself
If the valves and fittings are dry and water keeps appearing from under the tank or from beneath its outer jacket, the tank itself is probably leaking. The Smart Home Water Guide tells homeowners to look for leaks caused by corrosion, “such as a rusty water heater bottom.” ENERGY STAR’s warning signs also include visible corrosion and rust in the water.
A rusted-through tank can’t be patched. The City of Scottsdale’s water heater guide is blunt: “Once the tank rusts through, there is no way to repair it - replacement is the only solution.” ENERGY STAR warns that waiting too long risks “tank rupture and water damage to the floor and carpets.” A drip from the tank is a reason to call a plumber today, not something to watch for a few weeks.
Why tanks fail here: hard water and sediment
Phoenix-area water is hard. The City of Phoenix’s 2025 water quality report lists total hardness of 10 to 17.6 grains per gallon and says hard water “can cause some types of scaling in pipes and water heaters.” Other Valley cities report similar ranges: Chandler’s 2025 report lists 10.1 to 16.8 grains per gallon, and Scottsdale’s latest report lists 13 to 17.
Those minerals settle in the tank as sediment. The City of Scottsdale names “overheating from sediment build-up inside the tank” as a main cause of failure. A report written for the Department of Energy by Pacific Northwest National Laboratory (PNNL) adds that scale from highly alkaline water can lead to decreased equipment life in gas storage and tankless heaters. For storage heaters, its fix is to drain the tank every year to remove sediment.
The anode rod matters too. It’s a metal rod inside the tank that corrodes so the tank doesn’t. Scottsdale’s guide says replacing the anodes every 3 to 4 years “will add considerable life to a water heater,” and more often with softened water, because “softeners can cause the anode to wear out more quickly.” The PNNL report also notes that softened water raises the risk of corrosion.
How old is your water heater?
ENERGY STAR puts the typical life of a storage water heater at about 13 years. It says that if you suspect your heater is more than 10 years old, “it is time to consider replacing it before you’re left with an emergency decision.”
University of Florida IFAS Extension says most water heaters last 10 to 15 years, and the City of Scottsdale cites an industry average of 12. None of these figures is specific to Phoenix water.
If your water heater is in the garage
The City of Scottsdale’s guide says a garage water heater must be raised so the pilot, burners or heating element and switches sit at least 18 inches above the floor. That platform doesn’t keep a leak off the floor, and garage leaks spread in ways that are easy to miss:
- Across the slab. Water runs under stored boxes, bins and shelving. Cardboard soaks it up from below.
- Into the garage drywall. Water wicks up the bottom of the wallboard, often out of sight behind shelves.
- Into the house. If the heater sits against the wall shared with the house, or near the door into it, water can reach the base of that wall and the flooring on the other side.
If the leak reached rooms inside the house
When a heater sits in a closet or laundry room, or the water ran in from the garage, the leak goes straight into flooring. Carpet pad soaks it up, and water runs under laminate, wood and vinyl plank and into cabinet bases. The EPA says the subfloor under wet flooring must be cleaned and dried too.
The EPA also says wet drywall may be dried in place if there’s no obvious swelling and the seams are intact. Dry desert air dries surfaces, but it doesn’t reach water inside a wall cavity or under flooring. A provider uses moisture meters to find it.
Plumber, restoration provider or both
These are two separate jobs.
- A plumber repairs or replaces the water heater. That might be a new drain valve, fitting or relief valve, or a new heater if the tank has rusted through.
- A restoration provider deals with the water the heater let out. That means removing standing water, drying the structure and taking out drywall, carpet pad or other materials that can’t be saved. See emergency water extraction and structural drying.
You may need only a plumber if the water stayed on bare concrete, you caught it early and a mop took care of it. Call a restoration provider as well when:
- Water reached drywall, baseboards, cabinets, carpet, or wood or laminate flooring
- It spread into a room inside the house
- The leak ran for a while before anyone noticed
- You notice a musty smell or new stains near the heater
The EPA advises drying water-damaged areas and items within 24 to 48 hours to prevent mold growth. A slow leak behind a heater may have run much longer than that. Our guide to the signs of hidden mold lists what to watch for in the weeks after.
The jobs often overlap: the old tank may have to come out before the wall behind it can dry, so tell both who is doing what, and in what order. Before anyone starts, look up their contractor license with the Arizona Registrar of Contractors and get the scope of work in writing. Our page on water heater and appliance leak cleanup explains what the drying and repair work involves.
A word on insurance
The Insurance Information Institute says the common HO-3 homeowners policy covers accidental discharge of water from a plumbing system or household appliance, but excludes water seepage. The NAIC adds that a policy doesn’t pay to repair items that simply wear out, so the water damage and the heater itself may be treated differently. Check your own policy, and see our insurance guide.