Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns. As per your complain indigestion along with dirty water in mouth in your case seems to be due to Gastroesophageal reflux disease also known as Acid reflux.. The dirty water in mouth seems to be acid that refluxes from stomach to throat and mouth and can cause bad taste as well as indigestion.. Other causes of indigestion can be Gastric ulcers, stomach infection, irritable bowel syndrome etc.. White coating on tongue can be due to yeast infection known as Oral Thrush.. I would suggest you to consult a Gastroenterologist and get evaluated and a thorough clinical evaluation and investigations like colonoscopy, upper G.I endoscopy can help in diagnosis and treatment can be planned accordingly. He can advise you proton pump inhibitors like Omeprazole, antacids like Calcium Carbonate, avoiding spicy and heavy meals, doing moderate workout, taking more of yoghurt in diet, drinking warm water and sleeping with head slightly raised as compared to feet.. For white tongue consult an Oral Phsyician and in case if thrush is confirmed antifungal mouthwash like Nystatin mouthwash and clotrimazole lozenges and intake or probiotics like Yoghurt and garlic can help.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.