How would stomach react to water?

[jackson6612]

Stomach mainly produces gastric acid and pepsinogen. How would stomach react to water? Is gastric acid always present there in the stomach whether there is some food or not? If it is there all the time, then after the milk is drunk it would congest. Right? But would it produce pepsinogen though there are no proteins in water? If not, then how would it know that there are no proteins in water and it doesn't need to produce pepsinogen?