What Are pH, Alkalinity, and Corrosivity?
pH
pH measures how acidic or alkaline water is on a scale from 0 to 14. A pH of 7 is neutral. Below 7 is acidic. Above 7 is alkaline (also called basic).
Low pH water tends to be more aggressive toward metals. EPA notes that low pH can contribute to metallic taste and corrosion. (EPA)
Alkalinity
Alkalinity is not the same as pH. It measures water's ability to neutralize acids and resist pH changes. Think of it as a buffer. (USGS)
Low alkalinity water is less stable and can be more corrosive, even if the pH looks acceptable.
Corrosivity
Corrosivity describes how aggressively water attacks pipes and fixtures. It depends on pH, alkalinity, hardness, dissolved oxygen, temperature, and other factors. (USGS)
Two homes can have the same pH but very different corrosion problems if their alkalinity differs.
Why Corrosive Well Water Matters
The main concern with corrosive water is what it can do to your plumbing. Acidic, low-alkalinity water can:
- Dissolve lead from solder, brass fixtures, and older pipes
- Dissolve copper from copper plumbing, causing blue-green stains
- Cause pinhole leaks in copper pipes over time
- Create a metallic taste in your water
CDC warns that corrosive groundwater can cause lead to leach from pipes and fixtures, and that private well owners are responsible for testing since private wells are not regulated like public systems. (CDC)
Lead exposure is a serious health concern, especially for children. There is no safe level of lead in a child's blood. (EPA)
What Causes Low pH in Well Water
Well water pH depends on local geology and groundwater chemistry. Some regions naturally produce acidic, low-alkalinity water.
Common causes include:
- Geology: Certain rock types produce naturally acidic groundwater
- Rainfall: Rainwater is slightly acidic and can lower groundwater pH in high-recharge areas
- Organic matter: Decomposing vegetation produces acids that can affect shallow groundwater
- Lack of limestone: Regions without calcium-rich rock often have lower pH and alkalinity
pH can also change seasonally or after heavy rain. Installing treatment systems like reverse osmosis can sometimes lower pH, making water more corrosive.
When to Test for pH and Corrosivity
Consider testing if you notice:
- Blue-green stains in sinks or tubs (often from copper)
- Metallic taste in water
- Pinhole leaks in copper plumbing
- Fixture corrosion or discolored water
- Elevated lead or copper on a previous water test
Also test for pH and alkalinity:
- When moving into a home with a private well
- After installing new plumbing or fixtures
- Before and after installing water treatment
- As part of routine well testing every few years
CDC recommends pH as part of annual well testing. (CDC)
How to Test pH and Alkalinity
Laboratory Testing
For accurate results and treatment planning, use a certified lab. A water chemistry panel typically includes pH, alkalinity, hardness, calcium, and total dissolved solids. You can add lead and copper testing if corrosion is a concern. (CDC)
Test Strips and Meters
Home pH strips or handheld meters can give a rough idea of acidity but are less precise. pH can shift after collection, so minimize delay and follow instructions carefully.
Interpreting Corrosivity
There is no single number that defines "corrosive." Labs can calculate corrosion indices using pH, alkalinity, hardness, and other measurements. For private wells, the practical approach is to test the key parameters and interpret them together.
How to Interpret Test Results
pH
EPA's secondary guideline for pH is 6.5 to 8.5. Water below 6.5 is considered acidic and may be corrosive. (EPA)
However, corrosion can still happen within the recommended range if alkalinity is low.
Alkalinity
Alkalinity is reported in mg/L as calcium carbonate (CaCO3). There is no universal "ideal" level, but low alkalinity combined with low pH is a warning sign. Higher alkalinity helps stabilize pH and reduce corrosion. (USGS)
Low Mineral Content
EPA notes that water with high acidity or low mineral content is more likely to leach lead from plumbing. Low mineral content often means low alkalinity and low hardness together. (EPA)
What to Do About Acidic or Corrosive Water
Step 1: Reduce Immediate Exposure
If you suspect lead in your water, flush the tap for 1 to 2 minutes before using water for drinking or cooking. Use cold water only, since hot water can dissolve more lead. (CDC)
Step 2: Test for Lead and Copper
If your pH or alkalinity suggests corrosive conditions, test for lead and copper at the kitchen tap. This tells you whether metals are actually entering your water.
Step 3: Consider Neutralization Treatment
If pH is below 6.5 and you have corrosion symptoms, treatment can help. Common options include:
- Neutralizing filters: These use calcite (limestone) or a calcite-magnesium oxide blend to raise pH. They require periodic media replenishment. (CT DPH)
- Chemical feed systems: A pump injects soda ash or similar solution to raise pH. These require ongoing chemical purchases and monitoring. (VT DOH)
Note: Neutralizing filters add calcium or magnesium to the water, which can increase hardness.
Step 4: Retest After Treatment
After installing treatment, retest pH, alkalinity, and metals to confirm the system is working. Check periodically to ensure continued performance.
Prevention and Maintenance Tips
You cannot change your groundwater chemistry, but you can manage its effects:
- Flush before drinking: Run the tap for 1 to 2 minutes after water has been sitting
- Use cold water for drinking and cooking
- Clean aerators regularly to remove accumulated sediment and particles
- Maintain treatment systems according to manufacturer instructions
- Test periodically to catch changes before they cause problems
- Keep records of test results to spot trends over time
If you install a neutralizer, check media levels and replenish as needed. If you use chemical feed, monitor solution levels and adjust dosing if water quality changes.
Frequently Asked Questions
What pH level is safe for drinking water?
EPA recommends pH between 6.5 and 8.5 for drinking water. This is a secondary (aesthetic) guideline, not a health-based standard. Water outside this range may taste off and can cause corrosion problems.
Can low pH in well water cause lead poisoning?
Low pH water can dissolve lead from plumbing materials, which can lead to elevated lead in drinking water. This is especially concerning in homes with older plumbing or brass fixtures. Testing for lead at the tap is the best way to know your exposure.
Why does my well water have blue-green stains?
Blue-green stains usually indicate copper leaching from pipes. This happens when acidic, low-alkalinity water corrodes copper plumbing. Testing pH, alkalinity, and copper can confirm the cause.
What causes pinhole leaks in copper pipes?
Corrosive water is a common cause. Low pH, low alkalinity, and certain water chemistry conditions can gradually eat through copper pipes, creating pinhole leaks over time.
How do I raise the pH of my well water?
Neutralizing filters using calcite or limestone are the most common method. Chemical feed systems using soda ash can also raise pH. Work with a water treatment professional to choose the right approach for your water chemistry.
Is acidic well water safe to shower in?
Showering in acidic water is generally safe. The main concern is corrosion of plumbing over time and potential metal exposure through drinking water, not through skin contact during bathing.
How often should I test my well water for pH?
CDC recommends including pH in annual well testing. Test more often if you have corrosion symptoms, install treatment, or notice changes in water quality.