Pinhole Leaks in Copper Pipes: The Real Cause (And the Permanent Fix)

Caller "I have an older home with copper plumbing. I've had multiple pinhole leaks, and I'm not sure what the problem is."

Aidan "Get your pH tested. Find out how acidic the water is. Treat the water, and the pinhole leaks will stop."

That is how most of these calls start. The plumber has usually been out more than once, every patch held, and the next hole opened somewhere else. The pipe is not the problem. Something in the water is.

What causes pinhole leaks in copper pipes

A pinhole leak is the end of years of corrosion inside the pipe. The water dissolves copper off the inside wall until the wall opens at its thinnest spot. The way I explain it on the phone and in the video: as the water flows through the copper plumbing, it starts to create a channeling effect and dissolves the copper. The dissolved copper leaves blue-green stains in the tub or the shower or the toilet you use most often. Once that channeling gets to a certain point, it pops a pinhole leak and you have water everywhere. The EPA lists "corrosion of household plumbing systems" as the source of copper in drinking water; the stain and the leak are the same copper, going two places.

Copper does not corrode on its own. The Copper Development Association's Copper Tube Handbook calls corrosion of copper water tube "very infrequent" and lists six things that cause it when it does happen. In a house it is nearly always the water, and on a private well it is one thing in particular.

If you are on a well, see blue-green stains where water dries in the tub or shower you use most, and the leaks are on the hot lines first, your water is acidic. Below about pH 7 no protective film can form inside the pipe, so the bare copper keeps dissolving. Nearly every pinhole call I take from a well is this one, and copper pipe is only rated for water at pH 6.5 and above. Test the pH; under 7 confirms it, and how to stop the next pinhole leak is the fix.

Under four minutes on camera: why the pipe thins, the garden hose trick, and what stops the next leak.

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Text me a photo of the pipe or the stain, and your pH if you have one. I'll tell you whether the water is the cause and what to do about it.

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Why pinhole leaks keep coming back

Pinhole leaks keep coming back because the water is thinning every copper pipe in the house at the same time, and the patch only fixed the spot that opened first. You get a pinhole leak there, then a pinhole leak here. Each repair holds, because the plumber put new metal where the old metal gave out. But the water going through the new piece is the same water, and the rest of the run is still on its way to the same thickness. It shows first where the water works hardest: the fixtures you use every day, and the hot side, because heated acidic water is four to five times more aggressive than cold.

It can happen with a neutralizer in the basement, too. A caller in Connecticut in January had a backwashing neutralizer about fifteen years old. He had not serviced it in a year and was testing 6.5 to 6.8 after the tank. He had been getting pin leaks, luckily all down by the equipment and none in a wall. If the water is 6.5 coming out of the tank, the raw water is probably in the 5s. And a reading of 6.8 taken with no water running drops a good deal once the house is drawing water through the tank. A neutralizer that is too small for the pH, or that has not had its calcite topped up, is treating some of the water some of the time. That is why I usually recommend the 13 x 54 tank (the 2.5 cubic foot size) and why I tell every owner to check the calcite level once a year.

Is your water causing the leaks?

A pH strip from the hardware store tells you in a minute whether your water is under 7, and a certified lab test tells you the pH, how much copper is already in your water, and what else is going on. Go to Lowe's or Home Depot for a home pH test kit if you want the answer today, test the pH, and call me with the number and I can size a neutralizer accordingly. If you want the all-around test, the $199 lab test takes a couple of weeks and the results are extremely accurate.

What the number means:

• 7.0 or higher. The water is not dissolving your copper. Open the other four causes: a joint, a fast run, or pitting water on a city supply.
• 6.5 to 6.9. Acidic. Copper pipe is only certified for water at pH 6.5 and above, and I treat anything under 7. The Connecticut caller was at 6.8 with no water running and still getting pin leaks.
• Under 6.5. The handbook says this water "may require corrosion control." Plain calcite handles it down to pH 5.5 in the 2.5 cubic foot tank, and down to 6.0 in the 1.5.
• Under 5.5. Plain calcite is not enough on its own. The tank ships with a calcite and FloMag blend, mixed to your pH.

The copper number on a lab report tells you how much of the pipe is already in your water. Of the lab tests my customers send in, about one acidic tap in six had more copper than the EPA allows (10 of 62 under pH 7). At pH 7 and up it was about one in ninety. Too much copper in drinking water can upset your stomach in the short term and harm the liver or kidneys over years; the blue-green stains page has the chart and the health detail.

If you have not tested yet: certified lab test, $199

Test the water before the next repair

One certified lab test, mailed to you, run by an accredited lab, gives you the pH that says whether the water is the cause, the copper already at your tap, and the hardness and alkalinity that size the fix.

Get the certified well water test

53 contaminants. Results reviewed by Aidan, in plain English. On city water, use the city water test.

Finding a pinhole leak you cannot see

A hidden pinhole shows up as a damp spot, a stain, or a well pump that runs when nothing is on, and any of those means shut the water off and find it today. If you get one in the wall and you cannot see it, you are going to have thousands of dollars of water damage. Look for:

• A dark or soft spot on drywall, or a stain on the ceiling under a bathroom or a run of pipe.
• A drip mark or a blue-green crust with a wet center at one point on an exposed pipe. A dry crust at a joint, or a film along a whole cold line in summer, is a different thing; the green on the outside of the pipe section on the corrosion page sorts those out.
• The sound of water running when every faucet and appliance is off.
• On a well, the pressure gauge on the well tank. The pump only runs when water is leaving the tank, so with every faucet closed the needle should hold still and the pump should stay off. If the needle keeps falling and the pump kicks on, water is going somewhere. I have not had a caller run this check for a pinhole; it follows from how the tank works.

A leak you cannot reach is a plumber's job. Shut the main and make the call the same day; the water bill is not the cost, the drywall and the floor are.

How to stop a pinhole leak right now

Shut the water off, clamp a slit piece of garden hose over the hole, and have a plumber cut the section out; the patch buys you days, not years. People call me freaking out with water spraying in the basement, and this is what I tell them.

1. Shut the water off

   Close the valve nearest the leak if there is one. Otherwise close the main shutoff, which on a well is at the pressure tank and on city water is at the meter. Then open a faucet so the pressure drops and the spray stops.

   

2. Clamp garden hose over the hole

   Take a piece of garden hose, slit one side of it, wrap it around the pipe with the hole in the middle, put a hose clamp on it and tighten it up. That will stop the leak temporarily. Then turn the water back on and watch it. This is a patch for a few days, not a repair.

   

3. Have the section cut out

   The repair is a plumber cutting out the pitted section and putting new pipe in its place. Where the pinhole leaks occur, I tell people to replace that section with CPVC or PEX. If the copper cannot be moved to fit a normal coupling, a slip coupling slides over the ends. The visit is priced under what pinhole leaks cost to fix. Then test the water before the next one, so this repair is the last.

   

If the leak is inside a wall or a ceiling, skip the patch. Shut the main and call a plumber today, and leave the water off until the leak is found. A pinhole in the open costs a plumber visit. A pinhole behind drywall costs the drywall, the flooring and whatever the water reached.

How to stop the next pinhole leak

The next pinhole stops forming when the water stops being acidic, and a calcite acid neutralizer installed after the well pressure tank does that for the whole house. People ask what chemicals we use. We do not use chemicals. We use calcite, which is crushed limestone, in an upflow tank (the name just means the water comes up through the calcite). The water comes from your well tank, goes down the center tube, comes up through the calcite, slowly dissolves a little of it until it hits neutral, which is 7 on the pH scale, and moves on to the house line. The Copper Tube Handbook describes the same fix in its own words: "a bed of marble or limestone chips," raising the pH "to a value of about 7.2 or more." Put the treatment in and the corrosion of the plumbing and the water-using appliances stops, and no new pinholes start. Test first: if your pH comes back 7 or higher, this tank is not your fix.

Two things it does not do. It does not put copper back on the wall, so a section that has already pitted or leaked still needs the repair above; what changes is that the repair holds. And it does not care what the pipe is made of. A verified buyer with PEX plumbing wrote that her well water "had caused leaks to three PEX brass joints" before the tank went in. Another had her copper replaced with PEX and still had the plumber install the neutralizer, because the brass fittings, the water heater and every faucet still see the same water. Re-piping without fixing the water moves the problem; it does not end it.

Which tank depends on your pH, not on how many people live in the house; the pH lines for plain calcite and the blend are in the list above. The sizes, prices and refill schedule are laid out on how to stop copper pipe corrosion, the sizing guide walks through the numbers, and servicing an acid neutralizer shows the yearly check. Plan on a licensed plumber for the install; one verified buyer's plumber finished in about 3 hours and had to cut and refit the copper leading to the tank. I support your plumber by phone at 800-460-5810.

What pinhole leaks cost to fix

A plumber visit for one pinhole runs $300 to $500 or more, and the acid neutralizer that stops the next one is $1,195 to $1,495 shipped with the calcite. People ask me whether they should just call a plumber and get the leak fixed. You can do that, and for an active leak you have to. It is going to be probably $300 to $500 or more for him to come out and fix it; a caller in California who was pricing the work was quoted $85 to $125 an hour plus material, and a couple of hours is typical. My advice in the video is blunt: put that money into treating the water instead of paying a plumber to fix leak after leak. Your count may be two visits so far. The arithmetic is yours to do.

The neutralizer is $1,195 for the 1.0 cubic foot tank, $1,295 for the 1.5, $1,395 for the 2.0 and $1,495 for the 2.5, each shipped with the calcite; the calcite and FloMag blend for very low pH adds $200, and the backwashing model for water that also carries iron or sediment is $2,195. After that it is a $145 bag of calcite every 18 to 36 months depending on the tank size and your pH. You provide the fittings and piping for the install, and your plumber's time.

What buyers said after the leaks stopped

Every reviewer below is a verified purchase through our store; the quotes are as they wrote them.

Frequently asked questions