You have a freakish friend who only drinks pure distilled water. And keeps jars of them stored up in his basement.

When you went over to visit him, he offered you a glass. To prove to you how pure his water is, he got a pH meter and measured the pH. To his surprise, the pH was not 7!

Shouldn't the pH of pure water be 7 at 25 degrees? What happened? And was the pH greater or less than 7?