Water Can Be Purified by Many Ways, Including by Distillation

Essay

Water can be purified by many ways, including by distillation. A student distills water in a lab experiment, in which she is going to work with pH and acid/base properties. She obtains a pH meter, and discovers that her distilled water sample has an acidic pH reading. Knowing that neutral water should be neither acidic nor basic, the student assumes that the pH meter is not calibrated, but after calibrating it again, it reads a similar pH. What could explain the student's observations?