Did your petri plate grow bacterial colonies after you wiped the object with just water? Probably. This shows you that while plain water can help get rid of some microbes, it doesn't necessarily get rid of all of them. But you didn't grow too many microbes in the dish you swabbed after wiping the object down with your chosen disinfectant. Disinfectants are chemicals that kill microbes or at least lift them up off a surface so they can then be washed or wiped away. Disinfectants are one of the ways we can control microbial growth. Heat and cold are other means--you can sterilize water by boiling it and you can keep food from going bad by refrigerating or freezing it. Irradiation and antibiotics are other control methods.