washing face with water will increase skin's pH? will it break the skin's acid mantle?
If you switch to washing with water only... most of us live in areas of fluoridated water. Along with chlorine and numerous other contaminates. So if you go this route, you really only need to rinse your face. If you shower, and use shampoo, you might think about using either an all natural shampoo or baby shampoo, as these are much less irritating if they wash over your face.
But even water can be aggravating to certain skin types. It really depends on your supply and if you have filters. I never rubbed my face with water. I always just let the water run over it at warm temperature. And my showers don't last longer than 5 minutes, because i don't trust my water supply.
As far as acid mantle is concerned, it really depends on your method of washing. Hot or cold, rubbing or not, and condition of water supply. All these factors can play into whether or not you disrupt it. Cooler, with less rubbing, and from a clean supply (free of chemicals/contaminates) would be ideal for preserving the mantle. Though i don't think warm water will destroy it on it's own. But when you get into hot temps, it's easy for the oil to run off your face. Just like when you use cool water to rinse and oiled pan, it doesn't work. But hot water gets the oils moving and they run off much easier