tender coconut water is a fluid rich in salts like potassium, sodium,magnesium
etc. Hence they are good energy drink. It can reduce stomach acidity to a certain extent. But i suggest you to get evaluated so that your gastritis
is not caused because of infection by H Pylori or drug abuse
, ibubrufen. Also excessive smoking, alcohol consumption can cause gastritis, so only drinking tender coconut water wont benefit you much till the other causes are addressed. Take care.