Is one allowed to drink some water to swallow a medically prescribed pill on 17th of Tammuz?
It depends on the reason that you are taking the pill. If it is because you are not well, then you are allowed to take the pill with some water, because a person that is sick does not have to fast on 17th of tammuz, and this should be no less than that. However if the reason you are taking the pill is not because you are not well, then you can take the pill with some water, but it should be some type of water that you are not going to enjoy drinking, such as a black coffee, or a strong tea without sugar.
Have a refuah shleima