Uncontrolled watery stool after partial colectomy; is it normal and if so for how long?

Maybe. Could be infectious from c diff. Have that ruled out first. If that is negative you could take immodium or fiber wafers to treat and slow down transit of stool.
Depends. On which part of the colon was removed and how far out from your surgery. Right colectomies often associated with looser stools but should improve with time. Normal to have looser stools in the immediate post op period. Be sure to drink plenty of fluids to avoid dehyudration. I f still persisting after 4-6 weeks need to discuss with your surgeon or get another opinion.