Why is water coming from exhaust on a 1991 Chevrolet Suburban?

That is condensation due to the exhaust system being cold and the heat from the engine makes the exhaust system / pipes sweat. As the exhaust system heats up then that will stop.

Now you said WATER not antifreeze. If you had engine coolant running out of the exhaust then it would be the color of the antifreeze and it would be steaming WHITE and then you would have an engine problem, MAYJOR. You said water. Drive it you have no problems. That is normal.