Pipe corrosion is the slow chemical attack of your water on the metal carrying it, and the water side of the problem is treatable even when the plumbing side is not. Aggressive water with a low pH, dissolved oxygen or a high dissolved solids load will eat copper, galvanized steel and solder joints, and it usually tells you long before a pinhole leak does.
What makes water corrosive
Three things do most of the damage. Low pH water, common in soft surface supplies and in many shallow wells, is hungry for metal ions and takes them from the pipe wall. Dissolved oxygen and carbon dioxide accelerate that reaction. High total dissolved solids make the water more conductive, which speeds up galvanic corrosion wherever two dissimilar metals meet, most classically where a copper line was joined straight onto old galvanized steel without a dielectric fitting. Hot water lines corrode faster than cold ones because heat drives all of it.
Reading the signs before a leak
Blue green staining in a sink or tub is dissolved copper, and it points at acidic water attacking copper tube. Orange or brown staining with a metallic taste is more often iron from galvanized pipe or from the well itself. A bitter or metallic taste in the first draw of the morning, when water has been sitting in the pipes overnight, is a strong clue that the standing water is dissolving something. Pinhole leaks in copper, especially several in the same run, mean the process has been going on for years.
Test before you treat
The parameters that decide this are pH, alkalinity, hardness, total dissolved solids and temperature, plus a first draw sample for metals if you want to know what is actually leaving the pipe. If you are on a community system, the utility publishes an annual Consumer Confidence Report and the EPA maintains a finder for it, so you can see the treated water quality leaving the plant before it reaches your service line. On a well nobody does this for you, and our well water testing guide sets out the panel to order.
What treatment can actually fix
Acidic water is corrected at the point of entry with a neutralizing filter, usually a backwashing tank of calcite or a calcite and magnesia blend, which dissolves slowly and raises pH and alkalinity as water passes. It adds a little hardness in the process, which is why an acid neutralizer and a softener are often fitted together. Where the water is only mildly aggressive, a properly sized softener alone can reduce the conductivity driving galvanic attack. Media is topped up periodically, not replaced wholesale.
What treatment cannot fix
Treatment changes the water, not the pipe. If a run of galvanized steel is already scaled shut, or copper is perforated, no filter recovers it and the answer is repiping, which is a plumber job rather than a water treatment purchase. The sensible sequence is to correct the water chemistry first so the new pipe is not attacked the same way, then replace what has already failed. Fitting a neutralizer after a repipe is protecting the investment; fitting one instead of a repipe is not.
Questions people ask about pipe corrosion
Does a water softener stop pipe corrosion?
Not by itself. A softener removes hardness, which stops scale, but corrosion is driven mainly by low pH and dissolved gases. Acidic water needs a neutralizing filter to raise the pH before the pipe stops being attacked.
Are blue green stains dangerous?
They are a clear signal that your water is dissolving copper from the plumbing, which is worth correcting on both health and plumbing grounds. Test the first draw water in the morning, since that is when concentrations are highest.
Can I just use a whole house filter?
A sediment or carbon filter does nothing for corrosivity, because the problem is chemistry rather than particles. You need something that changes pH and alkalinity, which means a neutralizing media tank or a chemical feed system.
Is corrosion different on city water?
Often yes. Utilities usually add corrosion control at the plant to protect their own mains and your service line, so an in home corrosion problem on city water is more likely to come from mixed metals or old fittings inside the house.