How do I change the PH of water?

Water quality method: the pH
Water quality and pH are often mentioned in the same sentence. The pH is a very important factor, because certain chemical processes can only take place when water has a certain pH. For instance, chlorine reactions only take place when the pH has a value of between 6,5 and 8.

The pH is an indication for the acidity of a substance. It is determined by the number of free hydrogen ions (H+) in a substance.
Acidity is one of the most important properties of water. Water is a solvent for nearly all ions. The pH serves as an indicator that compares some of the most water-soluble ions.
The outcome of a pH-measurement is determined by a consideration between the number of H+ ions and the number of hydroxide (OH-) ions. When the number of H+ ions equals the number of OH- ions, the water is neutral. It will than have a pH of about 7.
The pH of water can vary between 0 and 14. When the pH of a substance is above 7, it is a basic substance. When the pH of a substance is below 7, it is an acid substance. The further the pH lies above or below 7, the more basic or acid a solution is.
The pH is a logarithmic factor; when a solution becomes ten times more acidic, the pH will fall by one unit. When a solution becomes a hundred times more acidic the pH will fall by two units.
The common term for pH is alkalinity.

Water quality method: the pH
Water quality and pH are often mentioned in the same sentence. The pH is a very important factor, because certain chemical processes can only take place when water has a certain pH. For instance, chlorine reactions only take place when the pH has a value of between 6,5 and 8.

The pH is an indication for the acidity of a substance. It is determined by the number of free hydrogen ions (H+) in a substance.
Acidity is one of the most important properties of water. Water is a solvent for nearly all ions. The pH serves as an indicator that compares some of the most water-soluble ions.
The outcome of a pH-measurement is determined by a consideration between the number of H+ ions and the number of hydroxide (OH-) ions. When the number of H+ ions equals the number of OH- ions, the water is neutral. It will than have a pH of about 7.
The pH of water can vary between 0 and 14. When the pH of a substance is above 7, it is a basic substance. When the pH of a substance is below 7, it is an acid substance. The further the pH lies above or below 7, the more basic or acid a solution is.
The pH is a logarithmic factor; when a solution becomes ten times more acidic, the pH will fall by one unit. When a solution becomes a hundred times more acidic the pH will fall by two units.
The common term for pH is alkalinity.

To balance pH, you can use either NaOH (to make a fluid more basic) or NaCl (To make a fluid more acidic).

(although, I wouldn't recommend consuming the water afterwards)

Yeah maybe. But the water will no more be called 'water' but rather a 'dilute solution'. Am I not wrong? However I don't think that you can change the pH of water without adding something to it with in a way 'changes' its nature.

You don't have to add to the water to change its pH, you can clean the water and remove its solution to make it more basic and pure and balanced. It depends on your base solution for your base line testing model. Is your water already acidic.