Pure distilled water has a theoretical pH of 7.0 — perfectly neutral. In practice, it almost always measures slightly below that. Here's why, and what it means for drinking.
The moment distilled water is exposed to air, it begins absorbing carbon dioxide (CO₂). That CO₂ dissolves into the water and forms carbonic acid, which releases hydrogen ions and lowers the pH below 7. The reaction:
CO₂ + H₂O → H₂CO₃ (carbonic acid) → HCO₃⁻ + H⁺
In practice, freshly distilled water exposed to air typically measures between 5.5 and 6.9. This is a natural chemical reaction — not contamination. The water is still pure.
This is the same process that makes rainwater slightly acidic (pH ~5.6). It's harmless.
pH Scale: Quick Reference
Water Type
Typical pH
Notes
Freshly distilled (sealed)
~7.0
Neutral before CO₂ absorption
Distilled (air-exposed)
5.5–6.9
CO₂ absorption lowers pH
Australian tap water
6.5–8.5
ADWG recommended range
8-stage KDF filtered water
7.0–8.5
Mineral stages raise pH naturally
Rainwater
~5.6
Same CO₂ absorption process
Is the Acidity of Distilled Water a Problem?
For most practical uses — drinking, CPAP machines, baby formula, steam irons — the mild acidity of distilled water is not a concern. Your stomach acid (pH 1.5–3.5) is vastly more acidic than distilled water, so the slight acidity has no meaningful effect on your body.
The one practical consideration: mildly acidic water is slightly more corrosive to metals. Store distilled water in glass or food-grade plastic containers, not bare metal.
How to Raise the pH of Distilled Water
If you want mildly alkaline distilled water for drinking, there are two simple options:
Magnesium prill beads — place a bag in your water container. They raise pH to approximately 7.4–8.0 and add beneficial magnesium. Browse our magnesium prill beads.
Maifan mineral stones — add trace minerals and raise pH naturally. Browse our Maifan stones.
Both options are used with our 8-stage KDF filter systems, which naturally produce mildly alkaline water through their mineral stages.
How to Accurately Test the pH of Distilled Water
Standard pH electrodes struggle with very pure water because there aren't enough ions for the electrode to work reliably — readings can fluctuate. To get a stable reading, add a few drops of potassium chloride (KCl) solution to the sample before measuring. This increases conductivity without changing the pH result.
For home use, pH test strips are the simplest option and accurate enough for most purposes.
Frequently Asked Questions
Is distilled water acidic or alkaline?
Freshly distilled water is neutral (pH 7.0), but exposure to air lowers it to approximately 5.5–6.9 due to CO₂ absorption. This is mildly acidic but harmless. To raise the pH for drinking, add magnesium prill beads or Maifan mineral stones.
Is it safe to drink slightly acidic distilled water?
Yes — the mild acidity of distilled water (pH 5.5–6.9) is not harmful. Your stomach acid is far more acidic (pH 1.5–3.5). For long-term daily drinking, remineralising distilled water is recommended to restore beneficial minerals.
