The water supply process of Nanning Water Supply Company can be expressed as: water inflow → sedimentation → filtration → adsorption → disinfection → water supply.

A, disinfection requires disinfection with disinfectants such as chlorine, and chlorine reacts with water to generate hydrochloric acid and hypochlorous acid to generate new substances, which belongs to chemical changes;

B, adsorption is the use of porous activated carbon, which can adsorb impurities, pigments and other substances on the surface without producing new substances, which belongs to physical changes;

C, filtration is a method of separating solid and liquid insoluble in liquid, but the mixture is separated and no new substance is generated, which belongs to physical change;

D, taking water changes the position of water, and no new substances are generated, which is a physical change.

As can be seen from the above analysis, only disinfection belongs to chemical changes, and others belong to physical changes, so we choose A.