Took out the water pump and a little piece of cast iron broke off where you screw in. Where could the piece have gone? The piece was part of the pump where the 3 screw holes are.
My car has 140000 miles.
My car has a manual transmission.
Are talking about a piece of the water pump or the mounting flange where the water pump bolts, too? If it is the water pump, then just make sure the piece did not fall into an engine open hole. Use a magnet to probe all holes and crevasses below where the hole was located to see if you find the piece. If it was a mounting flange for the water pump, then have a mechanic look at it to see if it is part of the engine block or another flange that can be replaced.