Hello, you should understand that stomach pain occur due to numerous reasons like gastritis, food allergies, food poisoning, constipation, lactose intolerance, gastroesophageal reflux disease, ulcers, indigestion one of this might be the cause for your problem. Based on the history you have given it might be due to gastrointestinal infection from the unclean water you are consuming. So I advice you to stop doing that. Get a opinion of physician for further management