Yes PVC glue is safe to use on water pipes supplying drinking water.
When you use PVC glue you put just enough on the PVC pipe and fitting to allow the PVC pipe to glue together.
You should not have any or at least very little of the PVC glue inside the water pipe where water flows.
If you do get some PVC glue in the water pipe when gluing the pipe together you need to run the water for 30 minutes or so to help clear out the PVC glue.
I have gotten a taste of PVC glue before out of an outdoor hydrant after I had just installed it.
So make sure you run the water for awhile before drinking the water if you did get a bit of PVC glue into the pipe.