Adding aluminum chloride to water decreases its pH through metal cation hydrolysis, a well-established chemical principle where hydrated aluminum ions release protons into the solution.
The claim is a fundamental chemical fact regarding the hydrolysis of Lewis acid metal cations like Al3+ in water, which releases hydrogen ions and lowers the pH. Papers 0, 3, and 7 discuss aluminum species hydrolysis or use aluminum chloride in aqueous media where these chemical properties are relevant, serving as partial supporting evidence. Since this represents standard textbook chemical behavior (common knowledge), a strict citation is not strictly required to validate the core chemical mechanism, but the available papers consistently align with the scientific principle.