Are you wanting the toolbox "look" for a sink or is there a practical reason? Those boxes are mobile and the plumbing less so..
My shop has plumbing inside of it, but no dedicated water source right now. Basically, I removed the Anti-siphoning on the exterior hose bib and we run water to the building from a hose.
We collect rain water off the building to the tune of thousands of gallons - it's pretty easy to do and the water tests much cleaner than local wells. Some of the hanger spaces in my area actually do water collection on the inside of the building from the outside. Depends on where you can place a tank.
Other options (like the other thread) are a simple water tank or RV water tank.
RV water pumps are 12V, around $80 or so. There may be simpler options. With a 1-20 gallon pressure tank, the pump will hardly run at all.
Here's our first water collection tank - you could, of course, scale this back: