So I have been working on the 'Sanctuary' quest. I am at the step of building a source of water and assigning a worker to the resource. I have gone to every settler and have commanded them to "go" to the resource to work, the'll walk over to it stand by it for three to four seconds and walk off. Anybody else having this issue, anybody have an ideas on how to fix?

You need to be in the build mode when you interact with a settler, then once you look directly at a resource it should go green like it would if you tried to move it around and it the command will say assign. If it says go you are just telling him where to move. There is a limit to how many resources one settler can take care of but you do not have to assign more manually, he will tend to similar resources until his max is reached. You can see which ones are assigned to him by focusing on him in build mode and they will light up green too.

I don't think the water purifiers and pumps need workers.