What do you think the pH of water is?

The pH of pure water is considered to be neutral so it has a pH of 7. However, if you have water that falls below this range, the solutions or substances are considered to be be more acidic than than normal water. On the other hand, if you have water above 7, it is considered alkaline or basic.

In the process of distillation, during condesation the temperature of water decreases Hence absorption of CO2 takes place and some H2CO3 is formed. This is an acid (though very weakly) so water turns acidic. Double distillation enhance this so theoritical pH is 7.0 but practically less than 7.0 (6.2 to 6.8)