pH is a measure of how acidic or alkaline your water is, expressed on a scale from 0 to 14. A pH of 7 is neutral, meaning the water is neither acidic nor alkaline. Numbers below 7 indicate acidity, numbers above 7 indicate alkalinity, and most drinking water falls somewhere between 6.5 and 8.5.
What pH Actually Measures
The letters “pH” stand for “power of hydrogen.” What pH really tracks is the concentration of hydrogen ions floating around in the water. More hydrogen ions means more acidity and a lower pH number. Fewer hydrogen ions means the water is more alkaline and the pH rises.
The scale is logarithmic, which means each whole number represents a tenfold change. Water with a pH of 5 is ten times more acidic than water with a pH of 6, and a hundred times more acidic than water at pH 7. This is why even small shifts in pH can have outsized effects on everything from pipe corrosion to aquatic life. Pure water, with no minerals or dissolved gases, sits right at 7.0.
What Changes Water’s pH
Water rarely stays at a perfect 7. The moment it contacts rock, soil, air, or plant life, its pH shifts. Dissolved carbon dioxide, whether from the atmosphere or from decaying organic matter, makes water more acidic. This is why rainwater typically lands below 7. Volcanic and andesite soils in regions like the Great Basin can push water pH even lower through natural weathering of acid-generating rock.
On the other end, water that flows through limestone or other alkaline minerals picks up compounds that raise pH. Algae and aquatic plants also push pH upward during daylight hours because photosynthesis consumes carbon dioxide and releases hydroxide ions. In lakes or ponds with heavy algal blooms, daytime pH can climb above 9 before dropping back down at night.
Typical pH of Different Water Types
Not all drinking water is created equal when it comes to pH:
- Tap water: typically around 7.5, though it varies by region depending on the local water source and treatment process.
- Bottled water: generally falls between 6.5 and 7.5.
- Distilled or reverse osmosis water: ranges from 5 to 7. Removing minerals strips away the buffering compounds that keep pH closer to neutral, and dissolved CO₂ from the air nudges it toward the acidic side.
- Bottled alkaline water: marketed at a pH of 8 to 9.
Why pH Matters for Your Health
The EPA recommends a pH range of 6.5 to 8.5 for drinking water. This is a secondary standard, meaning it’s a guideline rather than a legally enforced limit, but it exists for practical reasons.
Water that drops below 6.5 becomes corrosive. It can leach metals like lead, copper, manganese, and iron from your plumbing and well components. These metals are toxic in large amounts, and the risk is highest in older homes with lead solder or copper pipes. This is a real, well-documented hazard: acidic well water is one of the more common routes of chronic low-level lead exposure in rural areas.
Highly alkaline water carries different concerns. Your skin has a naturally acidic surface, with a pH between 4.0 and 6.0, that acts as a protective barrier. Exposure to water or solutions above pH 8.0 can cause skin proteins to swell and destabilize the fatty layers that hold moisture in. This is why very alkaline water can feel slippery on your skin and leave it feeling dry or irritated after prolonged contact. The damage to skin barrier lipids from alkaline exposure is actually more severe than from equivalent acidic exposure.
The Alkaline Water Question
Alkaline water with a pH of 8 or 9 has been heavily marketed as a health booster, but the clinical evidence behind most of those claims is thin. Your body tightly regulates its own internal pH through your lungs, kidneys, and blood buffering systems, and drinking slightly alkaline water doesn’t meaningfully shift that balance.
There are also safety concerns at the higher end. The Mayo Clinic notes that water with a pH above 9.8 has been linked to elevated potassium levels in the blood, a condition called hyperkalemia. This is particularly risky for people with kidney disease, whose bodies are less able to clear excess potassium. For most people, water in the 6.5 to 8.5 range is perfectly fine.
How to Test Your Water’s pH
If you’re on well water or just curious about what’s coming out of your tap, you have a few options. Paper test strips and liquid reagent kits, where you add drops to a water sample and compare the color to a chart, are cheap and widely available. They’ll give you a rough idea, but their accuracy is limited, especially in water with very low mineral content.
For reliable readings, a digital pH meter is the better choice. These use an electronic probe to measure hydrogen ion activity directly, and most consumer models are accurate to within 0.1 pH units. You can find basic versions for under $20. If you discover your water is consistently below 6.5, a neutralizing filter or calcite system can raise pH before the water reaches your pipes. If it’s above 8.5, your local water utility should be able to explain why and whether it’s a concern.