My Adult Son Seems To Be Reacting To The Drinking

My adult son seems to be reacting to the drinking water in Costa Rica and has been vomiting for 7 hours. I gave him a dose of Enterogermina, but it came right back up two minutes later. Gave him flat coke then flat gingerale, but he is not able to keep anything down. Tried to get him to eat a dry plain cracker, but he is not willing. Any suggestions?