Fasts for testing only, do not restrict water. In fact if you are dehydrated, some blood tests will be affected by that. BUN for example may test high when dehydrated. I've been told to drink water normally because it is also hard to pop the veins when you are dehydrated. Most maintenance drugs are allowed for blood testing...but you should ask to be sure. Most vitamins are reported as concentrations, ng/ml, for example. So if you are dehydrated they may show false higher readings.
The converse is also true, don't overdo any water, just enough to keep from being really thirsty.

Water is restricted before surgeries however, because of aspiration risk.

I wouldn't do anything with artificial sweeteners in it like gum.
There is just not enough evidence about them, but suggestions that they can affect blood sugar readings or insulin levels have been made. If you are having a fasting insulin taken exercise is not recommended as that will elevate it.