What is pH in well water?
pH measures hydrogen ion concentration on a logarithmic scale from 0 (extremely acidic) to 14 (extremely alkaline), with 7 being neutral. Most drinking water falls between 6 and 8.5. Natural groundwater pH varies based on the rock types it contacts: water flowing through limestone becomes alkaline (pH 7.5–8.5); water from granite or non-carbonate rock with limited acid buffering is often acidic (pH 5.5–7.0).
The EPA's secondary MCL (a non-enforceable aesthetic guideline) sets a recommended range of 6.5–8.5. Water below 6.5 is generally considered corrosive; water above 8.5 may have a bitter taste and scale-forming tendency.
Why does pH matter for well owners?
The primary concern is indirect: acidic water leaches lead and copper from plumbing.
- pH below 7 accelerates dissolution of lead from solder joints in homes built before 1986
- Acidic water corrodes copper pipes, causing blue-green staining and potentially elevated copper in drinking water
- Corroded pipes fail sooner, increasing plumbing maintenance costs
If you have acidic water and older plumbing, test for lead and copper in addition to pH. The pH problem may be a proxy for a lead problem.
Signs of corrosive water
- Blue-green staining on sinks and fixtures (copper corrosion)
- Metallic or sour taste
- Pinhole leaks in copper pipes
- Pitting on brass fixtures
Where is low-pH water most common?
Acidic well water is most common in New England, the Appalachian states, the Pacific Northwest, and the Southeast — areas with granite, gneiss, or non-carbonate bedrock that provides limited buffering capacity. Acid rain deposition (still significant in the Northeast) and CO₂ dissolution in groundwater (forming carbonic acid) both lower pH. Peaty soils contribute organic acids. Coal-affected areas (acid mine drainage) can have severely acidic water.
Testing
pH is best measured immediately at the tap with a calibrated pH meter or pH test strips. pH can shift significantly during sample transport as CO₂ outgasses, raising pH. Lab measurements are more accurate but may not reflect the actual pH at your tap. Include pH in any comprehensive water quality test.
Find a lab and learn how to test pH accurately
Treatment
- Calcite neutralizer filter — most common treatment; water flows through crushed calcium carbonate (calcite) media, dissolving CaCO₃ and raising pH to 7–8. Adds calcium hardness. Low-maintenance; media consumed gradually and replenished annually.
- Magnesium oxide neutralizer — similar to calcite but adds less calcium hardness; raises pH higher per unit volume; useful for very acidic water.
- Soda ash (sodium carbonate) or sodium hydroxide injection — chemical feed pump injects alkaline solution; precise pH control; better for very low pH or high flow; requires chemical handling.
- Acid injection — for high-pH alkaline water (less common); reduces pH for taste or specific treatment requirements.