Wow thats really quite harsh!! I've never had an employer refuse me my right to have water throughout the day! I always keep a bottle of water in the room and have a quick sip between patients, even my dentist does. And to dock wages or time in lieu is so unreasonable. If that was happening to me, I'd raise a formal complaint, especially if it was affecting my health. The other option of course is to find a nicer place to work where the employer is a bit more humane.