Well Water Leaves Green Stains on Fixtures – Copper Corrosion and Solutions

Green or blue-green stains on sinks, tubs, and fixtures are a telltale sign of copper corrosion in your plumbing system. These stains indicate that your well water is actively corroding copper pipes, releasing copper into your water supply. While the staining is unsightly, the underlying corrosion can also damage your plumbing and potentially affect your health.

Understanding what causes this corrosion helps you choose the right treatment to protect both your fixtures and your plumbing system.

What Causes Green Staining?

Low pH (Acidic Water)

The primary cause of copper corrosion is acidic water with pH below 7.0. Many wells, particularly in certain geological areas, produce naturally acidic water:

• Rainwater percolating through acidic soils
• Organic acids from decaying vegetation
• Carbonic acid from dissolved CO2
• Mineral-poor water that lacks buffering capacity

Acidic water is aggressive – it dissolves copper from pipe walls, which then deposits as blue-green stains where water sits or evaporates.

Low Alkalinity

Alkalinity measures water's ability to resist pH changes. Even water with acceptable pH can cause corrosion if alkalinity is too low:

• pH may fluctuate throughout the day
• Treatment or heating can shift pH downward
• Small pH drops cause aggressive corrosion

High Dissolved Oxygen

Water with high dissolved oxygen content corrodes copper more aggressively, especially when combined with low pH.

Electrical Grounding

If your home's electrical system is grounded to the water pipes (common in older installations), stray electrical current can accelerate corrosion through electrolysis.

Identifying the Problem

Classic Signs of Copper Corrosion

• Blue-green stains: On sinks, tubs, toilets, and anywhere water sits
• Metallic taste: Especially noticeable in first-draw water
• Green-tinted hair: Blonde hair can take on green tint (often mistakenly blamed on chlorine)
• Pinhole leaks: Eventually, corrosion creates small holes in copper pipes

Water Testing

Proper diagnosis requires testing:

pH: Should be between 7.0 and 8.5. Below 6.5 causes aggressive corrosion.

Alkalinity: Should be above 20 mg/L as CaCO3 for adequate buffering.

Copper: Elevated levels confirm corrosion is occurring. First-draw samples show highest levels.

Conductivity: Very soft, low-mineral water is often corrosive.

Treatment Options

Acid Neutralizers

The most common solution for acidic well water is an acid neutralizing filter containing calcite (calcium carbite) or a blend of calcite and corosex (magite):

• Water passes through mineral media
• Calcium and magnesium dissolve, raising pH
• Media must be replenished as it dissolves
• Also adds hardness to water (may require softening afterward)

These systems are effective, reliable, and widely used for corrosion control.

Soda Ash Injection

For severely acidic water or situations where added hardness is undesirable:

• Sodium carbonate (soda ash) solution injected into water
• Raises pH and alkalinity
• Adds sodium rather than calcium
• Requires chemical tank and injection system
• More maintenance than calcite filters

Polyphosphate Injection

Polyphosphate compounds coat pipe walls with a protective film:

• Creates barrier between water and pipe
• Effective for moderate corrosivity
• Doesn't change pH
• Requires ongoing chemical addition

Dielectric Unions

If electrolysis from electrical grounding contributes to corrosion:

• Install dielectric unions at water heater connections
• Separate electrical ground from water piping
• Consult electrician for proper alternative grounding

Cleaning Green Stains

While addressing the cause, you can remove existing stains:

For light stains:

• Vinegar or lemon juice (acidic cleaners)
• Baking soda paste
• Commercial bathroom cleaners

For stubborn stains:

• Bar Keeper's Friend (oxalic acid)
• CLR or similar products
• Cream of tartar paste

Prevention: Wipe fixtures dry after use to prevent water from sitting and depositing copper.

When to Call a Professional

Contact a well water specialist when:

• You notice persistent green staining
• Water testing confirms corrosive conditions
• You're ready to install treatment equipment
• Pinhole leaks develop in copper plumbing
• You want comprehensive water quality analysis
• Treatment isn't resolving the staining

We service all major pump brands including Franklin Electric, Grundfos, Goulds (Xylem), and Sta-Rite (Pentair). Our trucks carry common parts and components for same-day repairs.

Frequently Asked Questions