Water heater leaking? What to do right now (and what it'll cost)

A puddle under your water heater is one of those problems that looks minor until it isn’t. Water on the floor means you’re already past the “watch and wait” stage — the right move in the next ten minutes determines whether you’re dealing with a $200 repair or a flooded garage.

Shut off water and power first — here’s how

Before you poke around looking for the source, cut off the fuel and water supply. This takes under two minutes and it matters.

For a gas water heater: Find the gas shutoff valve on the supply line running into the heater — it’s usually within a foot of the unit. Turn the handle perpendicular to the pipe. Then find the cold-water supply valve at the top of the tank (it’s the one with a pipe running into the top, not out of the bottom) and turn it clockwise until it stops.

For an electric water heater: Go to your electrical panel first. Find the 240-volt double breaker labeled “water heater” and flip it off. Then shut the cold-water supply valve at the top of the tank the same way.

Don’t skip the power step on electric units. A heating element running without water around it will burn out in minutes — adding a $150–$300 repair on top of whatever was already wrong.

If the leak is significant — water actively running, not just a damp floor — and you can’t identify the shutoff valve quickly, turn off the main water supply to your house instead. You can sort out the rest once the water isn’t flowing. If you’re unsure whether a fast-moving leak qualifies as an emergency, our emergency plumbing page covers what rises to that level.

Once everything’s off, mop up the standing water so you can actually see what’s wet and what’s dry.

Where the leak is coming from tells you a lot

Dry the floor completely, then watch the unit for five minutes. The location of new moisture is your first real diagnostic clue.

Common sources:

• Cold or hot water inlet/outlet fittings at the top of the tank
• Pressure relief valve (T&P valve) — typically mounted on the side near the top, with a pipe running down toward the floor
• Drain valve near the bottom of the tank
• The tank itself — seam corrosion or internal failure

A fitting or valve leak is usually fixable. A leaking tank almost never is.

If water appears to be coming from the T&P valve — a brass valve with a lever you can flip up — don’t ignore it. That valve opens when pressure or temperature inside the tank exceeds safe limits. A little discharge during a heating cycle can be normal, but constant dripping or running means either the valve has failed or the tank pressure is genuinely too high. Both need attention from a licensed plumber, not a YouTube fix.

San Diego’s water is notoriously hard. The San Diego County Water Authority reports average hardness levels around 16–18 grains per gallon depending on your zone — well above the 7 GPG threshold that starts accelerating scale buildup and corrosion. That mineral load shortens valve life and eats at tank linings faster than softer-water regions. If your unit is older than eight years and showing any leak, the hard water context matters when you’re deciding whether to repair or replace.

Top of the tank vs. bottom of the tank leaks

Location on the tank narrows your diagnosis significantly.

Leaks at the top

Top leaks are usually good news, relatively speaking. The cold-water inlet and hot-water outlet connections sit up there, and both can develop slow drips from loose fittings, corroded nipples, or failed dielectric unions. These are accessible and repairable without touching the tank itself. A plumber can typically swap a corroded nipple or tighten a union fitting in under an hour.

The T&P valve also exits near the top on most tanks. If that’s your leak source, the valve itself costs $15–$40 in parts, and replacement labor runs $75–$150 in San Diego depending on access. Don’t try to test a T&P valve by repeatedly flipping the lever — worn valves often won’t reseat after you lift them, leaving you with a steady stream instead of a slow drip.

Leaks at the bottom

Bottom leaks are more serious. Three sources are possible:

Drain valve: The plastic or brass valve at the base is used to flush sediment. These valves degrade, especially if they’ve never been used and then opened once for a flush. A leaking drain valve can sometimes be fixed with a threaded cap over the outlet — a $3 part — or replaced outright for under $100 in labor.

Temperature and pressure discharge pipe: The pipe running from the T&P valve down to near the floor exits at the bottom. If this pipe is dripping, trace it back up to the valve — the valve is the actual problem, not the pipe.

Tank corrosion from the inside out: This is the one nobody wants. When the anode rod (a sacrificial magnesium or aluminum rod inside the tank) is depleted, the steel lining starts to corrode. Water seeping out of the seam, the base, or the insulation foam around the bottom almost always means the tank has failed internally. There’s no repair for that. Replacement is the only option.

If you’re seeing rust-colored water from your hot taps in addition to the leak, internal corrosion is almost certainly the cause.

When a leaking water heater can be repaired

Repairs make sense when the tank itself is intact and the leak is coming from a component you can replace. Specifically:

• Loose or corroded inlet/outlet fittings
• Failed T&P valve (valve is bad, pressure is otherwise normal)
• Leaking drain valve
• Corroded anode rod — replacing it before it depletes can extend tank life, though it won’t fix an active leak
• Faulty expansion tank on closed-loop systems (common in San Diego homes with backflow preventers)

Age is the biggest variable. Most tank water heaters last 8–12 years — we go deeper on that in our post on how long water heaters last. If your unit is under 7 years old and the leak is from a valve or fitting, repair almost always pencils out. If it’s 10+ years old, the repair math starts to look different even when the tank itself isn’t the source — you’re likely to be back here in 18 months with a different problem.

Our water heater service page covers both repair and replacement options if you want to get into specifics before calling.

When you need a full replacement

Replace the unit when:

• The tank is leaking from the seam, base, or through the insulation
• There’s visible rust or corrosion on the tank exterior (not just surface oxidation on fittings)
• You have rust-colored hot water
• The unit is 10+ years old and the repair cost exceeds 40% of replacement cost
• Your energy bills have crept up despite consistent usage — sediment buildup causes heating elements and burners to work harder

One number worth knowing: California requires any replacement water heater in San Diego to be strapped to the wall per seismic code. That’s not optional and it affects installation time and cost slightly, but every licensed installer here will handle it automatically.

If your current unit is a standard tank heater, a replacement is also a good moment to consider a tankless upgrade — better efficiency, longer service life, and no standing tank to corrode. The California Energy Commission offers rebate information for high-efficiency water heaters that can offset part of the upfront cost.

What water heater replacement costs in San Diego

Prices in San Diego run a bit higher than national averages, mostly due to labor rates and permit requirements. Here’s what to expect in 2025–2026:

Standard 40–50 gallon gas tank replacement: $1,100–$1,800 installed, including permit and haul-away of the old unit.

Standard 40–50 gallon electric tank replacement: $900–$1,500 installed.

Tankless gas unit (whole-home): $2,500–$4,500 installed, depending on whether gas line upgrades or venting changes are needed.

Tankless electric (point-of-use): $400–$800 installed.

These are real-world ranges, not lowball estimates meant to get someone in the door. The spread reflects variables like unit brand, access difficulty, whether your existing gas line is adequately sized, and whether the installation triggers additional code requirements in your jurisdiction. For more context on what drives plumbing labor costs here, see our breakdown of how much a plumber costs in San Diego.

Always verify your contractor is licensed before work begins. You can confirm a CSLB license in about 30 seconds at the California Contractors State License Board.

How to prevent the next leak

Most water heater failures are predictable. These habits extend unit life noticeably in San Diego’s hard-water environment:

Flush the tank annually. Sediment buildup from hard water insulates the bottom of the tank, forces the burner to run longer, and accelerates corrosion. A yearly flush takes 20–30 minutes and costs nothing if you do it yourself.

Check and replace the anode rod every 3–5 years. This is the most underrated maintenance item on any tank heater. When the rod is gone, the tank starts corroding instead. Replacement costs $20–$50 in parts plus an hour of a plumber’s time if you’d rather not do it yourself.

Install a water softener or whole-home filter. Given San Diego’s hardness levels, this is one of the highest-ROI plumbing upgrades you can make. It benefits your dishwasher, fixtures, and pipes, not just the water heater. Our water filtration service page has more detail on options.

Set your thermostat to 120°F. Higher temperatures accelerate mineral scale and increase T&P valve discharge cycles. 120°F is the EPA-recommended setting for water heater efficiency and safety.

Keep an eye on the T&P valve discharge pipe. If you see intermittent drips from that pipe without an obvious cause, get it looked at before it becomes a continuous problem.

A water heater that’s well-maintained in San Diego can realistically hit 12–15 years. One that never gets flushed and has a depleted anode rod might fail at 7 or 8.

When to call us

If the tank itself is leaking, you’re dealing with standing water, or you can’t identify the shutoff valves on your own, this is not a DIY situation. Active leaks near electrical panels or gas lines carry real risk, and a repair that seems simple can turn into a permit-required replacement depending on what a plumber finds inside.

Call us at (858) 465-7570 for a same-day estimate.