Which disinfection method does not alter the pH of the water?

The disinfection method that does not alter the pH of the water is ultraviolet (UV) disinfection. This process utilizes UV light to inactivate microorganisms by damaging their DNA, effectively preventing them from reproducing and causing disease. Since UV disinfection involves no chemical additions or reactions that can change pH levels, it maintains the water's existing pH balance.

In contrast, chlorination introduces chlorine into the water, which can lead to changes in pH depending on the residual chlorine concentration and the water's chemistry. Ozonation, which involves adding ozone gas to water, can also affect pH due to its chemical reactions in water. Filtration, while primarily a physical process to remove particulates, does not typically have a direct impact on pH either, but it may not be considered a disinfection method in the same context as UV or chemical processes. Thus, UV disinfection stands out for its ability to maintain pH while effectively disinfecting water.