Water Heater Leaking? Diagnosis Guide — All Leak Locations

Before touching anything, remove all standing water. Dry the top of the tank, all visible connections, the tank body, and the base completely. Use a flashlight to check the top fittings and the area around the T&P valve collar carefully.

• Water on top of the tank or at the cold inlet/hot outlet connections: Proceed to Step 2 (top leak diagnosis).
• Water at the side of the tank where the T&P valve mounts: Proceed to Step 3 (T&P valve diagnosis).
• Water at the base of the tank: Dry the floor and watch for where new water appears. Is it at the drain valve? At the end of the T&P discharge pipe? Or seeping from under the tank itself? Proceed to Step 4 (bottom leak diagnosis) or see the dedicated Water Heater Leaking From Bottom guide.
• Rust-colored water from the tank body: Tank corrosion — proceed to Step 4 immediately and plan for replacement.

A water heater leaking from the top almost always points to the inlet/outlet connections or the anode rod. These are the most accessible fixes on the unit.

• Check the cold water inlet and hot water outlet connections: Look for moisture at the threads, mineral buildup (white or orange crust), or active weeping at the dielectric union or brass nipple. Corrosion here means the fitting needs to be replaced — tightening won't help on a pressurized tank.
• Check flex connectors: Braided stainless flex lines fail at the swage fitting after 10–15 years. Bulging, corrosion at the fitting, or active weeping means replace the connector. Parts cost $10–30. If the tank nipples themselves are corroded, this becomes a plumbing job requiring a pipe wrench, thread sealant, and potentially a nipple extractor if the old fitting is seized.
• Check the anode rod: The anode rod screws into the top of the tank and is visible as a hex-head plug. If water is seeping around the anode rod hole at the top, the rod is fully corroded and the tank lining is next. This is a serious warning — a leaking anode rod port means the tank is actively corroding. Replacement requires draining the tank and threading out the old rod. Anode rod cost: $30–80.
• Look for a wet pan under the unit: If a drip pan is installed under the water heater and water is collecting in it, trace the source upward. The pan catches leaks from multiple sources — connections, T&P valve, drain valve, or tank body — so identify the origin before assuming it's the tank.

The temperature and pressure relief valve is a safety device mounted on the side of most water heaters. It has a lever to manually test it and a discharge pipe running down to within 6–12 inches of the floor. A leak at the T&P valve itself — not at the end of the discharge pipe — means one of two things:

• The valve is past its service life: T&P valves degrade over time. The rubber seat inside hardens, and the valve fails to reseat after opening. A T&P valve over 5–6 years old that drips at the collar should be replaced. Replacement part: $15–40. Labor to install: $75–150.
• The tank is overpressurizing: In a closed water system without a thermal expansion tank, the cold water supply valve prevents backflow and thermal expansion causes pressure spikes on every heating cycle. These spikes can push the T&P valve open repeatedly. Signs of this: the T&P discharges regularly, often at the same time each day or after a long heating cycle. Installing a thermal expansion tank ($150–300) addresses the root cause. If the incoming water pressure is above 80 PSI, add a pressure reducing valve ($200–400 installed) as well.

Water at the base is the most common water heater leak call. For the full diagnostic sequence, see our dedicated Water Heater Leaking From Bottom guide. The quick version is here:

• Drain valve: The plastic or brass valve at the base of the tank. Worn seat or debris prevents it from sealing fully. Test by watching the tip for 60 seconds; flush with a garden hose if you suspect debris. Replacement: $5–20 for a brass valve, DIY in 30–60 minutes.
• T&P discharge: If water appears at the end of the T&P discharge pipe (and not at the valve body itself), the T&P is venting — see Step 3. The discharge pipe routes water to the floor, so this looks identical to a base leak.
• Tank body corrosion: Rust-colored water or wet seams at the base of the tank body means the glass lining has failed and the steel tank is corroding from the inside out. This is not repairable. Check the serial number for age — Rheem, A.O. Smith, Bradford White encode the manufacture date in the serial. A tank over 10–12 years old leaking from the body should be replaced. Check the warranty before spending on repair.

Before spending on a repair, find the manufacture date on the serial number label (on the side of the tank). Most manufacturers encode this in the serial:

• Rheem and Ruud: Letter-number format. First letter = month (A=January, B=February, etc.); first two digits = year (e.g., G24 = July 2024).
• A.O. Smith: First four digits = year and month (e.g., 2406 = June 2024).
• Bradford White: Letter-decade format. Decode from the Bradford White serial chart (online or from the manufacturer).

If the unit is under 6 years old and leaking from the tank body, check the warranty — Rheem, A.O. Smith, Bradford White, and State all offer 6-year or 12-year tank warranties on residential units. If it's under warranty, call the manufacturer before paying for repair or replacement.