My settlements still seem to be glitched. If I already have water in my workshop, it doesn't seem to add more water. Plus, my food isn't being added to my workshop even when I have a lot of surplus food.

I think you are talking about the food and water the settlement want and needs. If I'm not mistaken, this isn't what you have in your workshop.

You have to plant crops and assign people to tend to them. You have to build water pumps of purifiers.

I do have people tending to the food. I have 59 food, 280 water. It adds 200 water to my workshop once in a while, but won't add anymore after that unless I take it out of the workshop. And my food isn't being added to the workshop at all.