Pinhole Leaks in Copper Pipes: Why Even “Good” Water Eats Plumbing

A pinhole leak is exactly what it sounds like: a tiny perforation that corrosion drills through the wall of a copper pipe, usually discovered as a stain on a ceiling or a musty smell in a wall. And here’s what surprises most homeowners — it happens on “good” water. Ordinary city water in the low-7 pH range can still pit copper over time. Plumbers see it constantly.

Why water attacks metal at all

All water is corrosive to plumbing metals to some degree — corrosion is just metal reverting to its natural mineral state. According to the Water Quality Association’s corrosion education materials, several factors speed it up: low pH (acidic water supplies extra hydrogen ions), dissolved oxygen, high mineral content (which raises electrical conductivity and feeds galvanic corrosion), high water temperature, and high flow velocity. None of those require “bad” water — they’re present in normal supplies in varying degrees.

City water and well water fail differently

On municipal supplies, water in the 7.2–7.5 pH range with dissolved oxygen can still pit copper — slowly, quietly, until a pinhole appears. On Hill Country wells, the bigger driver is often conductivity: highly mineralized water conducts the tiny electrical currents that drive galvanic corrosion wherever two different metals meet, which in a real plumbing system is everywhere. Higher temperatures make all of it faster, which is why leaks so often show up on hot-water lines first.

The old fix, and the modern one

The traditional approach on acidic well water was a neutralizer — a filter bed of calcite that dissolves into the water to raise its pH. It works, but it treats only one of the corrosion drivers and adds hardness back into the water while it does it.

The modern approach is the one municipal systems use: feeding a small, NSF-certified dose of phosphate that lays down a microscopically thin protective film on the metal itself. That is exactly what Active Armour® does — a corrosion and scale barrier that works at neutral pH. It is not an acid, and nothing about it makes water aggressive; it puts a shield between the water and your pipe. You can read more about how the chemistry works on our phosphate technology page.

What to do if you’ve had a pinhole leak

One pinhole is rarely alone — the conditions that caused it are systemwide. Before repiping the whole house, it’s worth a water evaluation: pH, hardness, and conductivity tell the story of why the pipe failed, and whether a protective treatment can stop the next one.

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