The reaction is:

Cl₂ + H₂O ⇌ HOCl + HCl

Hypochlorous acid (HOCl) is the primary disinfectant in chlorinated water. It is a strong oxidizer that kills bacteria and viruses by disrupting their cell membranes and enzymes.

While hydrochloric acid (HCl) is also formed, it plays a less significant role in disinfection.

It's important to note that the reaction is reversible. This means that the hypochlorous acid can break down back into chlorine and water, particularly in sunlight.