Pinhole leaks in copper pipes are usually worth repairing the first time and replacing the second. One pinhole can be cut out and replaced in copper. Two or more on the same run point to pitting along the whole pipe, and NYC's soft water, with an average Langelier index of −2.21, is corrosive. Older thin-wall copper fails first.
NYC Repipe & Repair publishes these figures with named sources so every number can be checked before you call anyone, including us.
A pinhole leak usually announces itself as a small stain on a ceiling, a hiss inside a wall or a fine spray from a pipe in the cellar. The hole is tiny, but it’s the visible end of corrosion working through the pipe wall from the inside. Whether to patch it or replace the pipe depends on how many there have been, where, and what kind of copper you have.
What causes pinhole leaks in copper
Copper pitting is less understood than it sounds. A peer-reviewed 30-year review in AWWA Water Science concluded that, despite decades of research, copper pitting is still poorly understood. It found evidence that, in soft waters, extra alkalinity or keeping pH below 8.5 may reduce pitting, that phosphate inhibitors may help in low-alkalinity water, and that biological processes are likely involved (Gibson and Karney, AWWA Water Science).
NYC’s water sits squarely in that soft-water category. DEP’s annual water quality report puts average hardness at about 25 mg/L, median pH at 7.3 and the average Langelier index at −2.21; a negative value means the water tends to dissolve metal rather than coat it (DEP’s annual water quality report). DEP adds orthophosphate, averaging about 2.2 mg/L, to protect pipes, mostly to control lead.
Other local factors stack on top:
- Thin-wall copper. Type M copper has a 0.032 in. wall at 3/4 in., against 0.045 in. for Type L (Engineering ToolBox). Less metal means less to corrode through. The current NYC code doesn’t list Type M for water distribution, but older work used it. See Type L vs Type K copper.
- Copper touching galvanized. Where new copper was screwed straight onto old steel, galvanic corrosion attacks the joint. PC 605.24.1 now requires a brass fitting, a dielectric fitting or an ASSE 1079 dielectric union.
- Fast water at fittings. Undersized pipe and sharp elbows erode copper’s protective film where flow changes direction.
Where NYC sees the most pinholes
Copper is the newer stock in most of the city, so pinholes cluster in postwar houses. On Staten Island, 68% of one- to four-family lots were built in 1960 or later, with a median of 1970 (MapPLUTO), and those houses were largely plumbed in copper. In older Brooklyn and Queens houses, pinholes often show up in copper added during past renovations, next to original galvanized. Read the color stripe on any exposed run: red marks Type M, blue Type L, green Type K.
How to repair one pinhole properly
- Shut the water at the main or the nearest valve, and drain the line.
- Cut out the damaged section, not just the hole. A pinhole rarely exists alone; looking inside the removed piece shows how deep the pitting goes.
- Replace it in Type L copper, soldered with lead-free solder (NSF/ANSI 372, PC 605.2) or joined with permanent press fittings. Removable push-fit couplings are prohibited for permanent work (PC 605.9).
- Fix the cause if one is visible, such as a copper-to-galvanized joint without a dielectric union.
If you can’t see where the water is coming from, water leak detection finds it before walls are opened. For the repair itself, see copper pipe repair. NYC price guides put an emergency leak repair at $500 to $2,000 before ceilings and floors are restored (Handyman NYC price guide). If it’s already spraying, follow what to do when a pipe bursts.
Repair or repipe: the decision
| What you’ve had | Usually the right call |
|---|---|
| One pinhole, the cut-out section is clean inside | Repair; keep an eye on it |
| One pinhole, the cut-out section is pitted throughout | Replace that run |
| Two or more pinholes on the same run | Replace the run, or the riser it’s on |
| Pinholes in different parts of the house | Plan a repipe |
| Pinholes plus Type M marking | Plan a repipe in Type L |
| Pinholes plus brown water or galvanized elsewhere | Repipe the whole system |
Each repair costs a plumber’s visit plus the ceiling or wall it came through, and each new leak can bring water damage. Homeowners policies generally cover sudden, accidental water damage but not replacing pipe that wore out; see is repiping covered by insurance?.
A full copper repipe in NYC typically runs $12,000 to $35,000 for a house and $3,000 to $8,000 for an apartment (repiping cost guide). Partial jobs cost less: pipe replacement for one run or one bathroom, or whole house repiping when the pattern is everywhere. The repipe assessment helps sort out which, and the repipe cost estimator puts a number on it.
Bottom line
Repair the first pinhole properly, in copper, and look inside the piece that comes out. If it’s pitted throughout, or a second pinhole appears on the same run, replace the run; if they’re showing up across the house, repipe in Type L. Call (929) 659-6658 for a free on-site estimate and a written, itemized price.