The short answer
Well water below pH 6.5 is acidic and can be corrosive, slowly dissolving copper and lead from household plumbing. Warning signs include blue-green stains, a metallic taste and, sometimes, pinhole leaks in copper pipe. Acidic groundwater is common in the NC Piedmont. A lab test confirms it, and an acid-neutralizing filter or chemical feed system is the usual fix.
What "low pH" means and why it matters
pH measures how acidic or basic water is, on a scale where 7 is neutral. EPA's secondary (aesthetic) guideline for drinking water is a pH of 6.5 to 8.5. Below that range, EPA lists a bitter metallic taste and corrosion as the noticeable effects.[source]
Low pH on its own isn't the main concern. The concern is what acidic water does to your plumbing. Corrosive water can dissolve copper from pipes and fixtures, and lead from older solder or brass fixtures.[source] That puts metals into your water that weren't in the well, and it slowly damages the pipes themselves.
How common acidic well water is around Charlotte
35%
Share of the Piedmont and Blue Ridge study area where groundwater pH missed the 6.5–8.5 range
Typically because pH was below 6.5. USGS sampled public-supply wells before treatment.
6.8
Median pH in 115 western and central NC bedrock wells
Slightly acidic to neutral (2009–2010 study, including Gaston and Lincoln counties).
5.8%
Union County private well samples outside pH 6.5–8.5, 2000–2011
2,985 samples tested through the state program.
USGS describes water below 6.5 as acidic and potentially corrosive.[source] The Charlotte region sits on these same crystalline-rock aquifers, so slightly acidic well water is a normal finding here, not a sign something is wrong with your well. It just needs to be measured and, when it's low, managed.
The warning signs
- Blue-green stains in sinks, tubs and toilets. EPA lists blue-green staining and a metallic taste as the signs of copper above its 1.0 mg/L secondary standard.[source]
- A metallic taste, especially in the first water out of the tap in the morning, when water has sat in the pipes overnight.[source]
- Small leaks in metal plumbing. Penn State Extension lists pinhole leaks among the signs of corrosive water.[source] Pinhole leaks can have other causes too, so a plumber should look at the pipe, and a water test should look at the water.
Soft water tends to be more corrosive than hard water at the same pH.[source] That's one reason labs often use an index such as the Langelier Saturation Index, which combines pH, hardness and other values to estimate corrosivity; a negative value indicates corrosive water.[source]
Copper and lead: what local well studies found
In a 2023 UNC study of 224 volunteer-sampled Union County wells, 14% of samples were above North Carolina's 1,000 ppb groundwater standard for copper, and 9% were above 15 ppb for lead. Those samples were collected after six or more hours without water use, and the report attributes the lead to household plumbing fixtures rather than groundwater.[source] In other words, the metals were coming from inside the homes.
That's why testing for corrosion has two parts. A raw-water test at the well measures pH and hardness. A "first-draw" sample from the kitchen tap after water sits overnight measures what your plumbing is adding.[source] For public water systems, EPA's action level for copper is 1.3 mg/L and for lead is 0.015 mg/L, with the lead level dropping to 0.010 mg/L starting November 1, 2027.[source] Those are useful yardsticks for a private well too. Our water testing service can set up both samples with a certified lab, and our guide to reading a well test explains how to compare results to the limits.
How low pH is treated
Because corrosion affects every pipe in the house, the fix goes where water enters the home.[source] There are two main categories:
| Feature | Acid-neutralizing filter | Chemical feed (soda ash) |
|---|---|---|
| How it works | Water flows through a tank of calcium carbonate (calcite) or magnesium oxide media that dissolves slowly and raises pH[source] | A small pump injects a soda ash solution ahead of the pressure tank[source] |
| Effect on hardness | Adds hardness (that's part of how it works)[source] | Doesn't increase hardness[source] |
| Upkeep | Media must be topped up as it dissolves; backwashing[source] | Refilling the solution tank and maintaining the pump[source] |
| Effect on water pressure | The media can lower pressure somewhat[source] | No pressure drop, since it feeds ahead of the pressure tank[source] |
Raising pH stops new corrosion, but it doesn't remove copper or lead that's already in the water from damaged pipes. If a first-draw test shows lead or copper above the action level, a point-of-use system certified for lead at the kitchen tap is a common addition while the corrosion is brought under control. Penn State notes that reverse osmosis, distillation and activated alumina can reduce these metals at a single tap.[source] See our reverse osmosis page.
Correcting pH often comes first in a larger plan, because many iron, manganese and arsenic treatments work better at the right pH. Our low pH and acidic water page explains how we sequence a system, and our iron and manganese guide covers the next step for many Piedmont wells. Neutralizers and feed systems connect to your plumbing; here's how licensed installation works.
Sources
- Penn State Extension, Corrosive Water Problems (2025)
- U.S. EPA, Secondary Drinking Water Standards: Guidance for Nuisance Chemicals (2026)
- U.S. EPA, National Primary Drinking Water Regulations (2026)
- NC Department of Environment and Natural Resources, Division of Water Quality, Naturally-Occurring Radon-222, Total Uranium, Radium-226, and Radium-228 in Drinking Water Wells in Western and Central North Carolina, 2009–2010 (Groundwater Circular 2011-02) (2011)