Copper in well water: stains and stomach upset
Copper usually comes from copper pipes when water is acidic. Above 1 mg/L it can leave blue green stains and a metallic taste; above 1.3 mg/L (EPA) it can upset the stomach.
- US (EPA)
- Action level 1.3 mg/L; cosmetic guideline 1.0 mg/L.
- Ontario / Canada
- Ontario aesthetic objective 1.0 mg/L; Health Canada maximum 2.0 mg/L.
What it is
Copper dissolves from pipes and fittings, especially when water is acidic or sits in the pipes overnight.
What your number means
- Within limitsBelow 1 mg/L
No concern expected.
- Worth a look1 to 1.3 mg/L
Stains and taste. Check your pH.
- Act nowAbove 1.3 mg/L
Over the EPA action level. Flush before use and fix the cause.
What to do
- Run the cold tap before drinking if water has been sitting.
- Check your pH; acidic water is the usual cause.
- Ask about a neutralizing filter, and test lead at the same time.
How often to test
Every few years, and after plumbing changes.
Common questions
What causes blue green stains?
Copper from your pipes, usually because the water is acidic.
Sources: EPA drinking water standards; EPA secondary standards; Health Canada drinking water guidelines. Limits checked October 2026.