Print drawing on water color paper, is it possible?
Laser printer toner is water resistant -- more so than most paper.  But the toner doesn't necessarily stick very well to papers other than office paper and specially coated materials. Toner can also look rather shiny.  So this could be a good option for your tests of different effects, but less so for the mixed digital/watercolour pieces.

Inkjets have the advantage of using ink which will look much more like the ink you'd expect especially on watercolour paper.  Some are water resistant, some aren't. I've got an epson that's over 10 years old now; the ink for that doesn't run on normal paper (though it does a little on photo paper).  There's a very slight solvent smell as the print comes out.  Printers I've used in the past have varied. 

You'll have to test on any printer you have in mind.  I suggest that you test on office paper using only the inks you want to use for your project -- probably just black, which would be a good thing as there should be fewer components to run (be sure to print using "black ink only" or a similar option; some printers use black and the coloured inks to produce black. You'll have to further test the printing on your watercolour paper, trying different paper options in the printer software.

If you're looking to buy a printer to do this, at least try to get a demo print on office paper and see what happens when you wet it.  The availability of T-shirt print transfers might be a minor guide as T shirts have to be washed, but the transfers might bond the ink to some extent.