Broken Bolt in Water Pump

is that a portion of the bolt sticking out of the housing?

If so, grab a nut that fits over the outer diameter and weld it onto the bolt.

Maybe take a drift and smack the end of the bolt. A little shock therapy sometimes breaks rusty stuff loose.

If you have room, cut the bolt so it doesn't have any burrs and slide the pump forward and off. That will give you plenty of exposed bolt to work with.