What does UV light do in water treatment?

The role of UV light in water treatment focuses primarily on its ability to disinfect water by eliminating harmful microorganisms, including bacteria, viruses, and protozoa. UV light achieves this by administering a lethal dose of radiation that disrupts the DNA or RNA of these pathogens, preventing them from replicating and thus rendering them harmless. This method of disinfection is highly effective and does not introduce any harmful chemicals or alter the water's chemical composition, which is an advantage over some other disinfection methods.

The other choices describe processes that are not related to the primary function of UV light in water treatment. While increasing water temperature is a physical change that can aid in certain treatments, it is not a function of UV treatment. Enhancing pH levels of water pertains to chemical adjustments, which UV light does not perform. Similarly, UV light does not directly remove heavy metals from water; this task typically involves different filtration or chemical processes. Therefore, the effectiveness of UV light in disinfecting water, particularly through the lethal disruption of microorganisms, makes this the correct answer.