Yes, drinking water will certainly change the pH of the stomach by a small amount. However, since your stomach is very acidic to begin with, drinking water will not dilute it significantly. Also, there are systems in place that alert the stomach when its acidity changes, and it consequently starts producing more acid to maintain its pH at a constant level.

Robert H.
Also, the acidity in the stomach works 2 fold. First, it denatures proteins to allow the proteases to do their job, cleaving the proteins into their smaller functional units. Also, it's part of the innate immune system. Most bacteria and viruses can't live/remain functional at a pH of 1.08/24/19