Shut off the cold water supply and the power/gas first. Do that before anything else. A leaking water heater can cause thousands of dollars in water damage within hours — and a running heating element in a partially drained tank can burn out or become a safety hazard.
Once the unit is off, you have time to figure out where the leak is coming from. That determines whether it's a $200 repair or a full replacement.
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Step 1: Shut it down (do this first)
Do these in order. Don't skip any — even if the leak looks small.
Turn off the cold water supply
Find the cold water inlet valve on top of the tank (usually a gate or ball valve). Turn it clockwise until it stops. This stops new water from entering, so the leak eventually drains out instead of running continuously.
Turn off the power or gas
Electric: Flip the breaker at your panel. Gas: Turn the gas control knob to "pilot" or "off." This prevents the heating element or burner from running in a tank that may drain below the heating zone — which can destroy the element or create a hazard.
Drain the tank if the leak is significant
Attach a garden hose to the drain valve at the bottom and route it to a floor drain or outside. Open the valve and let the tank drain. This reduces water pressure and minimizes further leakage.
Contain the water around the tank
Use towels, buckets, or a wet/dry vacuum. If the unit is on a finished floor, work fast — water spreads under flooring quickly. Photograph the leak and surrounding area for insurance records.
Don't run an empty or partially drained tank. If the tank is drained below the heating element and the power is still on, the element can burn out in seconds. Always shut off power or gas before draining.
Step 2: Find the leak source
Where the water is coming from tells you what you're dealing with. Dry the tank and fittings with a towel, then watch where water reappears.
| Leak Location | Likely Cause | Severity |
|---|---|---|
| Tank body (side or bottom) | Internal corrosion, cracked steel | Critical — Replace |
| T&P valve (side, near top) | Excess pressure or temperature, failed valve, missing expansion tank | Critical — Call Pro |
| Drain valve (bottom) | Worn valve, sediment damage, not fully closed | Moderate — Repairable |
| Inlet or outlet connections (top) | Loose fitting, failed dielectric union, worn nipple | Moderate — Repairable |
| Top fittings or nipples | Loose threading, corrosion at the connection | Moderate — Repairable |
| Condensation on the outside | Not a leak — condensation from a cold tank in a warm space | Not a leak |
Tank body leaks cannot be repaired. If the water is coming from the steel shell itself — not a valve or fitting — the tank has failed. It will only get worse. Plan for replacement.
Step 3: How serious is it?
Emergency — call a pro immediately:
- Leaking from the tank body
- Leaking from the T&P valve (pressure relief)
- Steam, hissing, or water near electrical connections
- Gas smell near a gas unit (leave the area and call the gas company)
- Water actively flooding a finished floor
Same-day service — not an active emergency:
- Slow drip from the drain valve
- Slow drip from inlet/outlet fittings
- Moisture around the top connections
- Minor seepage under the unit
Probably not a leak at all:
- Water only on the outside of the tank during cold weather — this is condensation
- Water on the floor near the tank but the tank is dry — check nearby pipes and the AC drain
- Water pooling only after hot water use — check the T&P valve and drain pan first
Leaking now? Get local help fast.
We connect San Dimas homeowners with independent local providers — 24/7.
Call (909) 488-7231Preventing water damage while you wait
If the tank is draining, you have some time. Use it well:
- Move valuables away from the area — boxes, furniture, rugs, electronics.
- Ventilate if it's a small enclosed space. Moisture leads to mold within 24-48 hours.
- Vacuum or towel up standing water as often as you can. Every minute counts on wood, laminate, and drywall.
- Turn off the water main if the supply valve won't stop the flow.
- Photograph everything — the leak source, the standing water, the affected flooring, and any damaged items.
- Don't step in standing water if you suspect electrical contact. Turn off the breaker first.
Homeowner's insurance tip: Most policies cover sudden water damage from a failed water heater — but not slow leaks you ignored. Prompt action and documentation make the claim easier.
Repairable vs not repairable
| Leak Source | Repairable? | Typical Cost (San Dimas) |
|---|---|---|
| Drain valve | Yes — valve replacement | $150-$350 |
| Inlet/outlet fitting | Yes — reseal or replace fitting | $150-$300 |
| T&P valve | Yes — replace valve and check expansion tank | $200-$450 |
| Top nipple/union | Yes — replace fitting | $150-$350 |
| Tank body | No — tank has failed | Replace: $1,200-$2,500 |
| Bottom of tank / base | No — tank has failed | Replace: $1,200-$2,500 |
If the tank is leaking, no amount of sealant, epoxy, or "tank repair kit" will fix it permanently. The steel has corroded through from the inside, and the leak will return — usually worse. Replacement is the only real fix.
Leaking water heater FAQs
Is a leaking water heater an emergency?
It depends on where it's leaking. A leak from the tank body is an emergency — it means the tank has failed and cannot be repaired. Leaks from the T&P valve or drain valve are usually repairable but should be addressed the same day.
Can a leaking water heater explode?
A leaking tank itself is not an explosion risk, but if the leak is caused by a stuck T&P valve or excessive pressure, that is a safety concern. Shut off the unit and call a professional immediately if you see a leaking T&P valve, steam, or hear hissing.
How much does it cost to fix a leaking water heater in San Dimas?
Repairable leaks typically cost $150-$450 depending on the source. If the tank body is leaking, the unit must be replaced — $1,200-$2,500 installed.
Should I turn off my water heater if it's leaking?
Yes. Shut off both the water supply and the power or gas. Running a water heater with a drained or partially drained tank can damage the heating element and create a safety hazard.
What causes a water heater to start leaking suddenly?
Common causes include a failed T&P valve, a worn drain valve, loose inlet or outlet fittings, corrosion in the tank body, and thermal expansion from a missing expansion tank.
Can I repair a tank leak with epoxy or a patch kit?
No. Tank leaks come from corrosion that has eaten through the steel from the inside. Any patch is temporary — usually a few days to a few weeks at best — and the tank will continue to fail. Replacement is the only permanent fix.
Does homeowners insurance cover a leaking water heater?
Most policies cover sudden water damage from a failed water heater but not damage from a slow leak that was ignored. Take photos and shut off the water fast — that helps the claim.