Pinhole Leaks in Copper
Updated February 20, 2026
Tiny holes from the inside out due to pitting corrosion. Start as small drips or green stains. One is a repair. Multiple are a warning that the entire system may be deteriorating.
Overview
Frustrating because they are unpredictable and often indicate systemic water chemistry issues, not a one-time failure. Microscopic pit on the inside deepens over months or years until it penetrates through. By the time you notice, water has already damaged drywall, insulation, or flooring. First one: cut and solder. Second or third within a few years? Corrosion is widespread. Conversation shifts to whole-house repipe.
Symptoms
- Small drip or fine spray from a copper pipe -- basement, crawl space, or inside a wall
- Green or blue-green stains on the pipe exterior -- developing pit, may not have fully penetrated yet
- Water stains on ceilings, walls, or floors below pipe runs -- hidden leak visible only through damage
- Slight pressure drop if multiple pinholes have developed
- Higher water bills with no change in usage -- 24/7 drip wastes thousands of gallons per year
- Mold or mildew near copper pipe runs -- hidden moisture creates ideal growth conditions
Common Causes
- Acidic water (pH below 7.0) -- dissolves copper from the inside. Lower pH means faster corrosion. Wells can be 5.5-6.0 without treatment. Municipal usually 7.0-8.5, but some regions are naturally acidic.
- Chloramine and dissolved oxygen -- chloramine (common municipal disinfectant) linked to accelerated pitting. High dissolved oxygen promotes oxidation. Creates deep, narrow pits in cold water lines.
- Dissimilar metal connections -- copper directly to galvanized without a dielectric union causes galvanic corrosion. Accelerates pitting at the copper side.
- High velocity and turbulence -- above 5-8 feet per second erodes the protective oxide layer. Common in undersized pipes, sharp elbows, and homes with pressure above 80 PSI.
- Age -- 20-50+ year old copper develops pinholes from cumulative corrosion even with normal chemistry. Hot water lines corrode faster.
What You'll Need
How to Fix It
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Apply an Emergency Temporary Repair
Water off to the affected pipe. Dry the surface. Pipe repair clamp (two-piece metal with rubber gasket), self-fusing silicone tape, or epoxy putty for very small holes. All temporary -- plan permanent repair ASAP.
Tip: Keep a repair clamp and self-fusing tape in your emergency kit. $5-10 each. Saves thousands in water damage by stopping a leak immediately. -
Permanent Repair: Cut and Replace the Damaged Section
Cut out 4-6 inches centered on the pinhole. Clean ends with emery cloth, apply flux. Replacement copper piece and two slip couplings. Solder all four joints with lead-free solder. Cool, water on, inspect. Requires soldering skills and propane torch.
Warning: Soldering near combustibles: heat shield behind the joint, fire extinguisher within reach. Many house fires are caused by plumbing soldering without fire protection. -
Alternative: Push-Fit Repair (No Soldering Required)
Not comfortable soldering? Push-fit (SharkBite) fittings. Cut, deburr, push on. O-ring and grab ring seal it. More expensive ($5-10 per connection vs $0.50 solder) but no fire risk, no special skills. Code-approved for permanent installation.
Tip: Pipe ends cut perfectly square and deburred smooth. Burr damages the O-ring. Deburring tool: $3-5, essential for push-fit. -
Inspect for Additional Pinhole Leaks
After the first repair, inspect all accessible copper. Green or blue-green stains indicate developing pits even without active leaks. Focus on horizontal runs, hot water lines, and dissimilar metal connections. Multiple areas with staining or active leaks? Corrosion is systemic. Individual repairs only buy time.
Tip: Flashlight and run your hand along pipes. Tiny drip may be felt as dampness even if not visible. Check both sides of elbows and tees where turbulence accelerates corrosion. -
Test Your Water Chemistry
More than one pinhole? Test water for pH, dissolved oxygen, chloramine, and Langelier Saturation Index (LSI). Negative LSI means corrosive water. Utility report, private lab, or water treatment specialist. Aggressive water? Whole-house neutralizer (calcite filter), phosphate injection (coats pipe interiors), or point-of-entry treatment.
Tip: Municipal water? Request the annual Consumer Confidence Report. Free. Includes pH and chloramine data. pH below 7.0 or chloramine use puts copper at higher risk. -
Evaluate Whole-House Repipe (If Corrosion Is Systemic)
Three or more pinholes within a few years, or widespread green staining? Whole-house repipe is the cost-effective long-term answer. Individual repairs become expensive and the risk of a catastrophic hidden leak grows. PEX: immune to corrosion, flexible, freeze-resistant, cheaper to install than copper. Typically 2-3 days, $2,000-10,000+.
Tip: Not in the budget? Replace hot water lines first. Hot water corrodes copper faster. Replacing just the hot side buys considerable time.
When to Call a Pro
Call a plumber if you are not comfortable with soldering or push-fit, if the leak is inside a wall, if multiple pinholes need system assessment, if you want a repipe estimate, or if the leak is on the main line requiring utility shutoff. Plumber can also test water chemistry and recommend treatment.
Prevention Tips
- Test water pH on wells or in regions with aggressive water. Below 7.0 accelerates corrosion. Whole-house neutralizer raises pH.
- Dielectric unions or brass transitions wherever copper meets galvanized. Prevents galvanic corrosion.
- Pressure below 80 PSI (50-60 ideal). Reduces velocity and turbulence that cause erosion-corrosion.
- Annual inspection of accessible copper for green stains. Early indicator of developing pits.
- Had one pinhole? Monitor closely. A second within a few years means systemic corrosion.
- Building new or repiping? PEX is immune to pitting, electrolysis, and acidic water attack.