Oh, sorry, I didn't realize you were back to the water question. The answer is, yes, you could refill those cartridges with water. They hold around 3 cc. You'd need to adapt the thingies that transfer insulin to the cartridge, but that would be pretty easy. Those things are used once and tossed in the original application but they probably would last for a while if you weren't concerned about sanitation.
The pump contains a single AAA battery and a tiny stepper motor, which drives a plastic screw that pushes on the end of a plunger, like a large syringe plunger. That feeds a small-bore flexible plastic hose, 24" long, typically, which can be cut off to make a "nozzle."
-- Ed Huntress