Is Your Stomach Acid (Gastric Acid) Diluted When You Drink Water?

Short answer: Yes, drinking a lot of water will certainly change the pH of the stomach, but this amount is trivial.

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.

When you drink water enough water, something known as the buffer capacity steps in. The buffer capacity of the stomach is the amount of secretion of hydrochloric acid needed to lower the pH to 3 when it increases above this value, usually after eating food or drinking too much water. In other words, when you drink too much water, buffering molecules inside your stomach begin losing protons, which increases the number of free protons in the system. In effect, these buffering molecules ensure that there is little variation in the normal gastric pH.