Gastric acid
The highest concentration that gastric acid reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.
Human viruses in water
The pH of most natural water is between 5-9. Enteric viruses are stable in these conditions. On the other hand, many enteric viruses are more stable at pH 3-5 than at pH 9 and 12. Enteroviruses can survive at pH 11-11.5 and 1-2, but for only short periods. Adenoviruses and rotaviruses are delicate to a pH of 10 or greater and leads to inactivation.