Water heater dripping from a pipe at the top
Likely a repair
The short threaded pipes screwing into the tank top are called nipples, and the connectors joining them to your household pipework are often dielectric unions. Both corrode where copper meets steel. That corrosion is the usual reason a top pipe drips, and it is a repair.
Scalding risk — the hot-side pipe and the water inside it can be 120 °F or more. Let it cool first.
How to tell it's this
- Green or white crust around a threaded joint at the top of the tank.
- The drip forms at the thread rather than running down from higher up.
- The joint is where a copper pipe meets the steel tank fitting.
- It has been getting slowly worse over months rather than starting suddenly.
What to do
- Shut off the cold water to the heater and run a hot tap to drop the pressure.
- Dry the joint and watch it for ten minutes to be sure which thread is weeping.
- Have a plumber replace the nipple or union rather than tightening it. Corroded steel threads snap, and a nipple that snaps flush with the tank usually means a new heater.
- Ask for dielectric unions or brass fittings on the way back together, which is what slows the corrosion down next time.
What it costs
With a plumber
Reseal or replace the leaking connector
$150–$400
installed
Part only
If a pro is already on site
$10–$50
the part itself
Typical US ranges for 2026, not quotes. Labour is 30–50% of an installed price, so where you live moves these numbers more than anything else does. Get two or three local estimates.
If that's not it
The wet spot is a hex plug rather than a pipe
The anode rod fitting →
Water is pooled on the jacket with dry fittings
Water pooling on top →
Not sure which of these it is?
Answer four questions — where it's leaking, tank or tankless, gas or electric, and how
old it is — for a specific cause, a repair-or-replace call, and a cost.