What Causes Pitting Corrosion in Plumbing Pipes?
Last updated October 31, 2026
The short answer
Why Pitting Starts
Pitting corrosion begins when the protective layer on the inside of a metal pipe gets damaged. That damage can come from water that is too acidic, too alkaline, or high in dissolved salts. Once the layer breaks, a small area of metal reacts with the water and starts to dissolve.
Oxygen plays a big role. Water with high dissolved oxygen speeds up the reaction at the pit site. Chlorine, often added to municipal water for disinfection, can also attack the metal if levels are high. Even small differences in water chemistry can create a tiny battery effect that eats a hole straight through the pipe.
Common Culprits in Water
Hard water with lots of calcium and magnesium can leave scale deposits. Under that scale, the metal stays wet and oxygen levels drop, which can set up a corrosion cell. Low pH water, below 6.5, is more aggressive and tends to strip away protective films.
High levels of chlorides, like those from salt-based water softeners, also encourage pitting. Sulfates and nitrates can play a part too. If your water has a metallic taste or leaves reddish or bluish stains on fixtures, that is a sign the pipes are corroding from the inside.
- Low pH water below 6.5
- High chlorine or chloramine levels
- Excess dissolved oxygen
- High chloride or sulfate content
- Scale deposits from hard water
- Stray electrical currents in the plumbing system
How to Spot It Early
Pinhole leaks are the main sign of pitting corrosion. You might see small water spots on walls or ceilings, hear a hissing sound from a pipe, or notice a musty smell from damp drywall. Check exposed pipes in crawl spaces, attics, and under sinks for tiny rust spots or crusty white or green deposits.
Also watch for a drop in water pressure or a sudden increase in your water bill, which can signal a hidden leak. If you see any of these signs, turn off the water supply to that area and call a plumber for an inspection. Early detection helps limit damage to your home.
What Repairs Usually Involve
For a single pinhole leak, a plumber can often replace a short section of pipe. If the corrosion is widespread, repiping part or all of the home may be necessary. The plumber will test your water to find the cause, then suggest treatment like a neutralizer or water softener adjustment.
After the pipe is fixed, any water damage to walls, flooring, or ceilings needs attention. The pros can inspect the affected areas, remove wet drywall or flooring, and dry everything properly. That helps prevent mold and further structural issues.
Long Term Prevention
Testing your water is the first step. A simple water test can show pH, hardness, chlorine, and dissolved solids. Depending on the results, you might install a pH neutralizer, a water softener set to the right level, or a whole-house filter. Regular maintenance of your water treatment system keeps it working.
Also, avoid letting water sit in pipes for long periods. Run taps regularly to keep water moving. If you have copper pipes, consider dielectric unions where different metals meet. If your pipes are old and prone to pitting, replacing them with a more resistant material like PEX may be the right long term answer.
Water damage does not wait
Water keeps spreading into floors and walls, so it is worth acting early. Calls are answered 24/7.
Call Now (281) 717-6340Frequently asked questions
Can pitting corrosion cause a pipe to burst?
Yes, pitting can create a pinhole leak that may worsen over time. If the pipe weakens enough, it can crack or burst, especially if water pressure is high. Regular checks and prompt repair of any leaks help prevent sudden failures.
Is pitting corrosion covered by home insurance?
Policies vary, and your insurer decides what is covered. Sudden water damage from a burst pipe is often covered, but gradual corrosion may not be. Check your policy and ask your insurance company about specific coverage for plumbing failures.
Should I replace all my pipes if I find pitting?
Not always. If only a few spots are affected, a plumber can patch or replace short sections. Widespread pitting in multiple areas suggests the whole system may be at risk. A plumber can assess the extent and help you decide the most practical option.