In some areas, tap water’s pH can range from 4-5 which is acidic. Clean water usually has a pH of 7 which is neutral. A study was conducted in 2017 on patients who were suffering from dry mouth and it was discovered that it was caused by the patients drinking unfiltered water. Drinking filtered water after meals and throughout the day helps to get rid of any acid and/or residue left in your mouth. It also helps to improve brushing your teeth.