Water Heater Leaking: What To Do

Water on the floor under a water heater does not always mean the tank is failing. Before scheduling a replacement, a licensed plumber identifies the exact leak origin — because each location carries a different repair path and cost outcome.

The four main leak locations are: (1) the temperature and pressure relief (T&P) valve on the side of the tank; (2) supply connections at the top of the tank (cold inlet, hot outlet); (3) the drain valve near the tank base; (4) the tank shell itself, typically the bottom seam or base welds. Only the last indicates the tank has failed internally.

A plumber will dry the area completely, then run the unit back to operating temperature to observe where moisture re-accumulates. Condensation on exterior surfaces — common in humid environments — can mimic a leak. Actual leaks will re-wet within 15–20 minutes of drying. Per IAPMO Uniform Plumbing Code §507, storage tank water heaters are required to have a properly functioning T&P valve and drain valve as standard installation equipment.

The temperature and pressure relief valve is a mandatory safety device on every water heater. It opens automatically when tank temperature exceeds 210°F or pressure exceeds 150 psi — conditions that, without relief, can cause catastrophic tank rupture. A T&P valve that drips or discharges water is not malfunctioning; it is doing its job.

The correct response to a weeping T&P valve is not to cap or replace the valve in isolation — it is to determine why the valve is opening. Two root causes: (1) the thermostat is set too high and the tank is overheating; (2) thermal expansion from a closed system (a backflow preventer or check valve on the supply without an expansion tank) is cycling pressure up to the relief setpoint. Both require professional diagnosis. Replacing the valve without addressing the cause will result in the new valve weeping as well.

Per CPSC Water Heater Safety Guidelines, T&P valve discharge pipes must terminate within 6 inches of the floor or route to a floor drain — never be capped or plugged. A plumber who recommends capping a weeping T&P valve should not be trusted with the repair.

If the T&P valve discharges heavily or continuously, shut off the water heater immediately (gas: turn dial to "pilot"; electric: cut the breaker) and call a plumber. This is an emergency condition. If the discharge pipe is missing entirely, that is a code violation — the valve has no safe termination point.

The drain valve is a hose-bib style valve near the base of the tank, used for flushing sediment during annual maintenance. These valves see infrequent use and the seat can fail or the packing can weep over years of thermal cycling. A slow drip from the drain valve is one of the lower-cost leak repairs on a water heater.

A plumber can replace a failed drain valve with the tank in place on most installations. The tank is shut down, the cold supply is closed, the tank is partially drained, and the old valve is removed and replaced — typically a 45-to-90-minute service call. Brass ball-style drain valves are preferred over the original plastic hose-bib valves that ship on many units; they are more resistant to thermal stress cracking.

Do not attempt to tighten a leaking drain valve stem without first confirming the valve design — some plastic drain valves will crack if torqued. If in doubt, cut the power/gas and cold supply and call a plumber rather than risk a sudden valve failure that releases the full tank volume.

Supply connections at the top of the water heater — the cold inlet and hot outlet — are a common leak point on tanks more than 8 years old. Dielectric unions and flex connectors are designed to isolate dissimilar metals (copper pipe to steel tank nipple), but the gaskets and seals in these fittings degrade over time under thermal cycling and water chemistry stress.

Hard water accelerates this failure. USGS water hardness data shows that much of the US Southwest, Mountain West, and parts of the Midwest have water above 120 mg/L (7 GPG) — sufficient to accelerate scale buildup on inlet fittings, increasing the risk of connection degradation. In high-hardness markets, dielectric unions should be inspected every 5–6 years.

Supply connection leaks are repairable without replacing the tank, provided the tank itself is in otherwise serviceable condition. A plumber replaces the failed fitting with new dielectric unions or corrugated stainless flex connectors — usually a 1–2 hour job. If the tank nipples (the short threaded steel pipes entering the top of the tank) are corroded, the repair becomes more involved, and the condition of the rest of the tank should be evaluated before investing in nipple replacement.

A leak from the bottom of the tank, from weep holes at the base, or from the seam where the tank shell joins the base assembly indicates internal corrosion. All residential water heater tanks are glass-lined inside — the glass liner prevents the steel shell from contacting water directly. When the glass liner cracks (from thermal shock, sediment stress, or anode depletion), rust forms on the interior tank wall and eventually breaches the shell.

There is no repair for a breached glass-lined tank. A liner repair is not possible — the tank must be replaced. Attempting to extend a leaking tank's life with patch compounds or pressure reduction is not a recognized repair method and will not hold under operating temperatures and pressures.

Per DOE Water Heater Efficiency and Replacement Guidance, standard residential tank water heaters have a design life of 8–12 years. A bottom-seam leak on a tank older than 10 years is almost always accompanied by sediment buildup, anode rod depletion, and reduced efficiency — conditions that make replacement clearly the correct economic decision.

When replacing a failed tank, EPA Energy Star certified water heaters include high-efficiency storage tanks and heat pump water heaters that qualify for the federal residential energy credit under IRS Energy Efficient Home Improvement Credit (25C) — worth up to $600 on qualifying storage units and $2,000 on heat pump models. A plumber familiar with the credit requirements can specify compliant equipment at installation.

Shut off the water heater and cold water supply immediately if any of the following are true: the leak is actively flowing rather than dripping; the water on the floor is significant enough to reach walls or cabinets; the T&P valve is discharging continuously; the leak location is the tank base or bottom seam; there is rust-colored water in the discharge.

For gas units: turn the thermostat dial to "pilot" or "vacation" mode first, then close the cold supply valve. Do not turn the gas supply off at the unit unless you smell gas — relighting a pilot on an older unit can be difficult without a plumber present. If you smell gas, leave the home and call your gas utility before calling a plumber.

For electric units: switch the breaker to the water heater circuit off first, then close the cold supply valve. An electric element exposed to air inside a partially drained tank will burn out in minutes — cutting power before draining protects the element if partial draining is needed to access the leak point.

Do not use the hot water system while a tank leak is active. Continued demand will cycle the burner or element, increasing internal pressure and potentially worsening the leak rate before the plumber arrives.

Every glass-lined storage water heater contains a sacrificial anode rod — a magnesium or aluminum rod threaded into the top of the tank. The anode corrodes preferentially, protecting the tank's steel shell from the same chemical attack. When the anode is fully depleted, the tank shell begins corroding from the inside, accelerating the failure timeline toward a bottom-seam breach.

Standard anodes last 3–5 years in average conditions; soft or acidic water (common in the Pacific Northwest and Northeast) depletes them in 2–3 years. Sediment accumulation accelerates depletion by trapping corrosive minerals against the tank bottom. A tank with a depleted anode and significant sediment buildup can develop a bottom-seam leak years before its rated design life.

Why this matters for leak diagnosis: a plumber performing a supply-connection repair or drain-valve replacement on a tank over 6 years old should inspect the anode condition as part of the service call. If the anode is more than 50% depleted (less than ½ inch of core wire exposed), replacement adds $50–100 in parts to the service call and can extend the tank's remaining service life by 3–5 years. If the anode is completely depleted and rust is visible on the tank shell interior (sometimes visible through the anode port), that is a strong signal the tank is within 1–2 years of a liner breach regardless of the current leak type.

Per DOE Water Heater guidance, annual sediment flushing and periodic anode inspection are the two highest-impact maintenance actions for extending tank service life. Most homeowners do neither — making anode depletion a silent accelerant in most early tank failures.

The right call depends on the combination of leak type, tank age, and repair cost. Use this framework:

Tank age under 6 years

Repair virtually any non-shell leak — drain valve ($75–150 labor), supply connections ($150–300), T&P valve (after diagnosing root cause). At under 6 years, the tank has significant remaining life and repair costs are well below replacement value. Exception: a bottom-seam leak on any tank at any age is a replacement event.

Tank age 6–10 years

Repair if: single-point failure (drain valve or supply connection only), anode rod still has service life, no sediment noise during heating cycles, no rusty water. Consider replacement if: repair cost exceeds $250, multiple components are failing, anode is depleted, or the tank is an older 3.5+ GPF design (a heat pump water heater upgrade at this point captures the $2,000 federal tax credit).

Tank age 10+ years

Replacement is the correct economic call for any repair exceeding $150. A 10+ year tank is past its design midpoint; the repair defers the eventual replacement by 1–3 years at most, and does not restore efficiency that has degraded from sediment and anode depletion. Per DOE Water Heater Efficiency guidance, tanks at this age typically operate at 15–20% below their rated efficiency due to sediment acting as an insulating layer on the heating element or burner surface.

Cost comparison

• Drain valve repair: $75–150 (parts + labor)
• Supply connection repair: $150–350 (fittings + labor)
• T&P valve + root cause diagnosis: $150–300
• Anode replacement (add-on during service): $50–100 parts
• Standard tank replacement (40–50 gal gas or electric): $800–$1,800 installed
• Heat pump water heater (HPWH) installed: $1,600–$3,000 before the $2,000 federal 25C tax credit — net cost often $1,000–$1,500 after credit on qualifying installs per IRS Energy Efficient Home Improvement Credit (25C)

Standard residential storage water heaters — gas or electric — are typically warrantied for 6–12 years and have a design life of 8–15 years depending on water quality, anode maintenance, and installation conditions. The year of manufacture is printed on the rating plate (usually on the side of the tank near the top), and the serial number typically encodes the manufacture date in the first four digits.

BuildZoom contractor cost data shows water heater replacement costs running $800–$1,800 installed nationally for standard 40–50 gallon gas or electric tanks — varying by tank capacity, fuel type, and local labor rates. Per BLS Plumbers, Pipefitters & Steamfitters wage data (OES 47-2152), median plumber labor rates range $28–$48/hour nationally, with higher rates in coastal metros and lower rates in secondary markets.

A water heater older than 10 years with a repairable leak (drain valve, supply connection) still warrants a replacement conversation. A repair that costs $200–$400 on a tank that has 1–2 years of life remaining is a poor investment relative to replacing the unit now while planning is possible — rather than during an emergency when the tank finally fails completely. A plumber can assess the anode condition and internal state during the service call and give an honest service-life estimate.

CDC Legionella Water Management Programs recommends maintaining hot water storage temperature at 120–140°F to inhibit Legionella bacterial growth. Water heaters set below 120°F — often done to reduce scalding risk — can create hospitable conditions for Legionella in the stored water column. This is an additional reason to not defer replacement when a tank is at or past design life.