What is the pH of distilled water?

With few exceptions, the pH of freshly distilled water will test between 6.8 and 7.0 (neutral) on the pH scale. If distilled water sits in an open container (exposed to air in other words) it tends to absorb carbon dioxide from the air. This will result in a gradual lowering of the pH due to the formation of a weak carbonic acid. Through this process the pH can get as low as 5.5 on the pH scale. This is of little consequence since carbonic acid at this level is only slightly ionized and is therefore very weak. This does however make the distilled water more aggressive in the dissolving of light metals such as copper and is one of the reasons copper should not be used to store or plumb distilled water.

For consumptive uses the dissolved carbon dioxide may actually be a benefit in that it tends to discourage the regrowth of bacteria from the air. It also gives distilled water an improved taste. (Remember that carbon dioxide is deliberately pumped into carbonated drinks at very high levels for the same reason.)

As far as the affects of steam-distilled water on the body, I recommend that you look at what Andrew Weil, M.D. has to say on the matter, “As far as acidity goes, distilled water is close to a neutral pH and has no effect on the body’s acid/base balance. Distilled water is safe to drink, and the kind of water I use myself.”