Soap is able to clean hands and dishes because of some pretty nifty chemistry. Soap molecules have on one end what’s known as a polar salt, which is hydrophilic, or attracted to water. The other end of the molecule is a nonpolar chain of fatty acids or hydrocarbons, which is hydrophobic—meaning that it’s repelled by water but attracted to grease and other oily substances. When you wash your hands, the soap forms something like a molecular bridge between the water and the dirty, germ-laden oils on your hands, attaching to both the oils and the water and lifting the grime off and away. Soaps can also link up with the fatty membranes on the outside of bacteria and certain viruses, lifting the infectious agents off and even breaking them apart. Once the oily dirt and germs are off your hands, the soap molecules thoroughly surround them and form tiny clusters, known as micelles, that keep them from attaching to anything else while they wash down the drain.
While it is true that you can get some dirt and germs off with just water and the friction of your hands, soap really does do a better job.