If your water heater is leaking, shut off the power and the cold-water supply immediately, then figure out where the water is coming from. That second step is what determines everything else.

Electric unit: flip the breaker labeled “water heater” in your panel.
Gas unit: turn the gas control knob to the PILOT position.
Cold-water supply: close the valve on the pipe running into the top of the tank (turn clockwise).
If you smell gas: do not touch any switches. Leave the house, leave the door open, and call your gas utility from outside.
Contain the water: set a bucket under the drip, lay towels, or run a wet/dry vac — but only after power is confirmed off.

The location of the leak tells you whether you’re looking at a repair or a replacement. Drips from fittings, valves, or connections at the top or side are usually fixable. Water pooling directly under the center of the tank, or rust-colored water seeping from the tank body itself, almost always means the tank has corroded from the inside and needs to be replaced.

A.O. Smith’s manufacturer guidance is clear: even a small leak under pressure can escalate to major water damage and mold quickly. Treat it as urgent regardless of how minor it looks right now.

Why is my water heater leaking?
What should you do immediately after finding a leak?
How do you find exactly where the leak is coming from?
Can you fix a leaking water heater yourself?
When does a leaking water heater need to be replaced?
What will a licensed plumber do when they arrive?
How do you prevent water heater leaks in the future?
How long will a leaking water heater last, and what does repair vs. replacement cost?
Key Takeaways
What the right call actually looks like from the field
Same-day water heater service in the Phoenix area
Useful sources

Why is my water heater leaking?

Understanding the cause starts with where the water appears. The tank is a pressurized vessel with several external components, and each location points to a different failure mode.

Top of the tank

Leaks at the top almost always trace back to the cold-water inlet or hot-water outlet connections. These threaded fittings can loosen over time from thermal cycling — the constant expansion and contraction as the tank heats and cools. Dielectric unions (the short fittings that prevent galvanic corrosion between copper and steel) are a common culprit. You’ll often see rust streaks or white mineral deposits around the threads before the drip starts.

Side of the tank

The temperature and pressure (T&P) relief valve sits on the side, usually with a discharge pipe running down toward the floor. A drip from this valve is not always a sign that the valve itself has failed. Industry guidance consistently flags T&P discharge as a symptom of a deeper problem: household water pressure that’s too high, a thermostat set above safe limits, or thermal expansion in a closed system. Replacing the valve without diagnosing the root cause leads to the same problem repeating.

Bottom and center of the tank

This is where the diagnosis gets serious. A few possibilities:

Drain valve drip: the plastic or brass valve at the base can weep if the washer wears out or sediment lodges in the seat. Often fixable.
Condensation: on a new tank or in humid conditions, surface moisture can look like a leak. Dry the tank completely and watch — if moisture returns evenly across the shell, it’s condensation.
Internal tank corrosion: sediment accumulates at the bottom of the tank over years of use, creating hotspots that damage the glass lining and accelerate corrosion of the steel shell. Once that shell is breached, water pools directly under the center. This is not repairable.

Leak location	Likely cause	Repair or replace?
Top fittings/connections	Loose unions, corroded threads	Usually repair
Side (T&P valve)	Valve failure or high pressure/temp	Repair valve + diagnose cause
Bottom (drain valve)	Worn washer or sediment in seat	Usually repair
Center/underside of tank	Internal corrosion, tank breach	Replace

Other contributing factors include high household water pressure (above 80 psi stresses tank seams and T&P valves), failed element gaskets on electric units, and loose fittings that were never fully tightened at installation.

What should you do immediately after finding a leak?

Work through these steps in order. Speed matters, but safety comes first.

Drain the tank if flooding is a risk — Attach a garden hose to the drain valve at the base of the tank and run it to a floor drain or outside. Open a hot-water faucet somewhere in the house to let air in so the tank drains properly.

Never attempt to work on gas supply lines, gas valves, or live electrical components yourself. These are licensed-plumber and licensed-electrician territory. The risk of electrocution or gas ignition is real, and a mistake compounds the damage.

Pro Tip: Before you call a plumber, photograph the data plate on the side of the tank. It shows the model number, serial number, and manufacture date. Most techs can tell from the serial number alone how old the unit is and whether parts are still available, which can save a diagnostic trip.

How do you find exactly where the leak is coming from?

A flashlight and a dry rag will get you most of the way there. The goal is to isolate the exact drip point before calling a pro, so you can describe it accurately and avoid unnecessary guesswork on arrival.

Dry the entire exterior of the tank with a towel, then wait five minutes and watch with a flashlight. This separates a real leak from surface condensation.
Check the inlet and outlet connections at the top. Look for wet threads, rust-colored streaks, or white calcium deposits. A slow drip from a union fitting often leaves a mineral ring around the joint.
Inspect the T&P valve and its discharge pipe. A small drip from the valve body itself may mean the valve has failed. Active water flowing through the discharge pipe points to a pressure or temperature issue in the system. Whirlpool’s troubleshooting guidance recommends only briefly lifting the T&P lever to test it — and only when the water is cool and you’re standing clear of the discharge pipe.
Look at the drain valve stem. A weeping drain valve sometimes responds to a gentle quarter-turn clockwise with pliers. If it keeps dripping after that, the valve needs replacement.
Check the center underside of the tank. Ponding water directly beneath the tank’s center, especially if it’s rusty or discolored, is the clearest sign of an internal breach. Leaking from the base of a tank is widely recognized as a signal of serious internal failure.

Pro Tip: If you genuinely can’t tell whether it’s condensation or a slow leak, tape a dry paper towel to the suspect area and check it in 30 minutes. A real leak leaves a wet spot in one location; condensation leaves the whole surface slightly damp.

Can you fix a leaking water heater yourself?

Some leaks are straightforward homeowner repairs. Others will make things worse if you try to DIY them. Here’s how to tell the difference.

What you can reasonably attempt

Tighten loose inlet/outlet connections. Use an adjustable wrench to snug up unions or threaded fittings at the top. Don’t overtighten — a quarter-turn past hand-tight is usually enough.
Replace a leaking drain valve. Drain the tank completely first, then unscrew the old valve and thread in a new brass ball valve with Teflon tape on the threads. This is one of the most common homeowner-accessible repairs, and the parts cost under $15 at any hardware store.
Reseal threaded fittings. If a fitting is dripping at the threads, drain and depressurize the tank, unscrew the fitting, wrap the threads with two layers of Teflon tape, and reinstall.
Replace a T&P valve (intermediate skill level). This requires draining the tank below the valve level, unscrewing the old valve, and threading in a new one rated to match the tank’s BTU and pressure specs. Only attempt this if you’re comfortable with basic plumbing and have the right PPE.

Tools you’ll need

Adjustable wrench and pipe wrench
Teflon (PTFE) pipe tape
Garden hose for draining
Bucket and wet/dry vac
Needle-nose pliers
Flashlight

What to leave alone

Any work on gas supply lines or gas control valves
Welding, patching, or epoxy repairs on the tank body
Internal tank components (anode rod replacement is fine; anything involving the tank shell is not)
Live electrical connections on electric heaters

If the tank body itself is wet, stop. Attempting DIY repairs on a corroded tank can trigger a sudden, larger water release and significantly more property damage. Call a licensed plumber.

A note on T&P valve replacement: the valve is a safety device, not just a plumbing fitting. A T&P valve that keeps discharging after replacement almost certainly means the system pressure or thermostat is the real problem. Swapping the valve a second time without addressing that is wasted money and a safety risk.

When does a leaking water heater need to be replaced?

Repair makes sense when the failure is in an external component — a valve, a fitting, a gasket. Replacement makes sense when the tank itself is the problem, or when the unit is old enough that a repair just delays the inevitable.

Signs that point clearly to replacement:

Water pooling under the center of the tank, especially if it’s rust-colored
Visible rust blisters or corrosion on the tank shell
Repeated T&P valve discharges even after the valve was replaced
Rusty or discolored hot water at the tap (indicates internal corrosion)
The unit is more than 10 years old and showing any of the above

The age rule: tank water heaters commonly last 8–12 years. According to NACHI’s life expectancy data, the typical service life for a conventional storage water heater falls in that range. A 12-year-old unit with a leaking tank body is not a repair candidate — the cost of parts and labor rarely justifies it when the rest of the tank is equally aged.

Cost trade-off: a drain valve replacement might run $100–$200 in parts and labor. A T&P valve swap is similar. A full tank replacement, including the new unit, labor, disposal of the old tank, and any code upgrades required, typically runs $800–$1,800 depending on tank size, fuel type, and local labor rates. Regional variation is significant, so get a written quote.

Check the data plate before committing to a repair on an older unit. If the warranty has expired and parts availability is limited, replacement is almost always the smarter financial move.

What will a licensed plumber do when they arrive?

A good technician won’t just replace the part you point to. Here’s the standard diagnostic sequence and what you can do to make the visit faster.

Typical workflow on arrival:

Confirm gas and electrical safety before touching anything
Locate and verify the leak source (they may dry the tank and watch, just as you did)
Test the T&P valve and check system pressure with a gauge
Inspect the anode rod and element gaskets if accessible
Check for corrosion on the tank body and base
Recommend repair or replacement with a written estimate

When a tech recommends same-day replacement: if the tank body is breached, corrosion is extensive, or the unit is past its service life, most licensed plumbers will recommend replacement on the spot. Having your model and serial number ready means they can often confirm parts availability or order a replacement unit before they arrive, avoiding a second trip.

Photographing the data plate, the leak source, and any visible water damage before the technician arrives is one of the most practical things you can do. It gives the tech a head start on diagnosis, helps confirm the unit’s age and warranty status, and documents the damage for any insurance claim you might file.

What to have ready before the tech arrives:

Photos of the data plate (model, serial, manufacture date)
Photos of the leak location and surrounding damage
Warranty paperwork if you have it
Clear access to the shutoff valves and the electrical panel or gas control
Any notes on how long the leak has been present

What to expect on the invoice: a diagnostic or service call fee, parts and labor for the repair or replacement, disposal fees for the old unit (often $50–$100), and a permit fee if your jurisdiction requires one for replacement. Ask upfront whether the quote includes all of these.

Pro Tip: Ask the technician to test household water pressure while they’re there. A gauge on an outdoor spigot takes two minutes and can reveal whether high pressure is stressing your plumbing system beyond just the water heater.

How do you prevent water heater leaks in the future?

Most water heater failures are predictable. A short annual maintenance routine catches the problems that cause leaks before they cause damage.

Flush the tank once a year. Sediment at the bottom creates hotspots that erode the glass lining and accelerate internal corrosion. Attach a hose to the drain valve, run it to a drain, and flush until the water runs clear. This is the single highest-impact maintenance task you can do.
Inspect the anode rod every 2–3 years. The anode rod is a sacrificial magnesium or aluminum rod that protects the tank from corrosion. Once it’s depleted, the tank corrodes instead. Replacement costs under $50 in parts and extends tank life significantly.
Test the T&P valve annually. Lift the lever briefly to confirm it opens and reseats cleanly. A valve that drips after testing, or that won’t open at all, needs replacement.
Check household water pressure. Test with a gauge on an outdoor spigot and aim for 50–60 psi. Pressure above 80 psi stresses tank seams and accelerates T&P valve wear. If your pressure runs high, a pressure-reducing valve (PRV) or thermal expansion tank is worth the investment.
Do a visual check every few months. Look for rust, moisture, or mineral deposits around fittings. Catching a slow weep at a union fitting early costs almost nothing to fix.
Schedule a professional tune-up and keep a log of maintenance dates. That log matters for warranty claims and for a buyer’s inspection if you ever sell the house.

Staying on top of annual plumbing inspections is one of the most reliable ways to catch developing issues before they become emergencies.

Pro Tip: Write the installation date on a piece of tape and stick it to the tank. It’s faster than decoding the serial number, and every technician who ever works on the unit will thank you.

How long will a leaking water heater last, and what does repair vs. replacement cost?

The honest answer: a tank with an external leak (valve, fitting) can last years more after a proper repair. A tank with an internal breach has an unpredictable remaining life measured in days to weeks, not years. Once corrosion has punctured the steel shell, the rate of deterioration accelerates.

Lifespan benchmarks:

Typical tank water heater: 8–12 years
A unit past 10 years with any corrosion signs: prioritize replacement over repair
A unit under 6 years with a valve or fitting leak: repair is almost always the right call

Ballpark cost ranges (U.S. national averages — regional variation applies):

Repair type	Typical cost range	Notes
Tighten/reseal fittings	$100–$200	Often included in a service call fee
Drain valve replacement	$100–$200	Parts are inexpensive; labor varies
T&P valve replacement	$100–$200	Includes diagnosing pressure/temp cause
Element gasket (electric)	—	Requires draining and some disassembly
Full tank replacement	$800–$1,800	Unit + labor + disposal + permits

A streaming leak from the tank body, significant rust blistering, or a third failure in the same component within a year all point to immediate replacement. Continuing to run a failing tank risks flooding, mold, and structural damage that costs far more than a new unit.

Insurance note: homeowners insurance often covers sudden and accidental water damage from a leaking water heater, but typically not gradual leaks or maintenance-related failures. Document the damage with photos and timestamps as soon as you discover it, and call your insurer before any major cleanup or repairs begin. Knowing what common plumbing failures look like can help you describe the situation accurately to your adjuster.

Key Takeaways

A leaking water heater is almost always repairable if the source is an external component, but a breach in the tank body means replacement, and age is the deciding factor when the call is close.

Point	Details
Shut off power and water first	Turn off the breaker or gas control, then close the cold-water supply valve before anything else.
Location determines outcome	Top and side leaks (fittings, valves) are usually repairable; center/bottom tank leaks typically require replacement.
Age is the tipping point	Tanks older than 10 years with any corrosion signs are replacement candidates, not repair candidates.
Annual maintenance prevents most leaks	Flush sediment, inspect the anode rod every 2–3 years, test the T&P valve, and keep pressure at 50–60 psi.
Empire Plumbing and Air Conditioning	Offers same-day water heater repair and replacement across Phoenix, Gilbert, Peoria, and surrounding areas (ROC 342717 & 342718).

What the right call actually looks like from the field

There’s a pattern that shows up repeatedly in water heater calls: a homeowner discovers a puddle, assumes the worst, and either panics into an unnecessary replacement or, more dangerously, ignores it because the drip seems small. Both reactions cost money.

The location-based diagnostic rule in this article exists because it reflects how licensed plumbers actually triage these calls. A drip at a union fitting is a 20-minute fix. A rust-stained puddle under the center of a 13-year-old tank is a replacement, full stop. The difference between those two outcomes isn’t the size of the puddle — it’s where the water is coming from.

What gets overlooked most often is the T&P valve situation. Homeowners replace the valve and consider the problem solved. But a T&P valve that keeps discharging is the system telling you something about pressure or temperature, not just about the valve. Addressing the symptom without the cause is one of the more common ways a water heater problem turns into a recurring expense.

The other thing worth saying plainly: a 10-year-old tank that develops a fitting leak is still a 10-year-old tank. The repair might be straightforward, but the unit is approaching the end of its expected service life. Getting a replacement quote at the same time as the repair quote is not pessimistic — it’s how you make an informed decision rather than a reactive one.

Same-day water heater service in the Phoenix area

When the leak is more than you want to handle alone, Empire Plumbing and Air Conditioning responds the same day across Phoenix, Scottsdale, Glendale, Peoria, Anthem, Mesa, Tempe, Gilbert, and surrounding communities. Licensed under ROC 342717 and ROC 342718, the team handles everything from a leaking drain valve to a full water heater installation when the tank is past saving.

Before the technician arrives, have these ready:

Photos of the data plate (model, serial, manufacture date)
Photos of the leak source and any visible water damage
The unit’s approximate age and any warranty paperwork
Clear access to the shutoff valves and the breaker panel or gas control

For emergency water heater repair in Phoenix, call Empire Plumbing and Air Conditioning directly. Same-day appointments are available, and the team arrives prepared to repair or replace based on what the unit actually needs, not what’s easiest to quote.

Useful sources

These manufacturer and industry pages are worth bookmarking, especially if you’re filing an insurance claim or need to verify warranty terms.

A.O. Smith: Why Is My Water Heater Leaking? — manufacturer guidance on emergency steps and leak causes
Rheem: 5 Signs Your Water Heater Is Going Bad — replacement indicators from a major manufacturer
Whirlpool Water Heaters: Leak Troubleshooting — condensation vs. leak diagnostics and pressure guidance
NACHI: Life Expectancy of Home Components — industry reference for appliance lifespan benchmarks
U.S. Department of Energy: Water Heating — efficiency and maintenance guidance from a federal source

Keep a photo of your unit’s data plate with these links. If you ever need to file a warranty claim or describe the unit to an insurer, having the model and serial number on hand saves time.

Water Heater Leaking: What Homeowners Should Do Now

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