B, in the method of purifying water, the water obtained by distillation is almost the highest purity water, but distilled water does not contain trace elements and minerals needed by human body, so drinking distilled water for a long time is not good for the body, so B is wrong;

C, China's per capita available fresh water resources are very few, so we should save water. Therefore, C is correct;

D, activated carbon has adsorption, adsorption odor and pigment, adsorption with activated carbon can not reduce the hardness of water, so D is wrong;

So choose: C.