The pH value of a sample of multiple-distilled water is

The pH value of multiple-distilled water is very near to seven. In pure water, a process called autoionization occurs where water molecules spontaneously dissociate into hydronium (H₃O⁺) and hydroxide (OH⁻) ions [2]. At a standard temperature of 25°C, the equilibrium constant (Kw) for this reaction is 1.0 × 10⁻¹⁴, resulting in equal concentrations of H⁺ and OH⁻ ions at 1 × 10⁻⁷ moles per liter. This balance yields a neutral pH of exactly 7. While distilled water is used in laboratories as a neutral control, exposure to atmospheric carbon dioxide can slightly lower the pH to around 5.5–6.0 due to the formation of carbonic acid. However, multiple distillation is a purification process intended to remove such impurities and ions, bringing the water's chemical state as close as possible to the theoretical neutral point of seven.

Sources

1. [2] https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:acids-and-bases/x2eef969c74e0d802:introduction-to-acids-and-bases/v/autoionization-of-water-ap