Please help: 1990 750 overheating. Suggestions?

Shortly after running our 750 it starts overheating. It does have enough water after we added water(but not antifreeze).
What suggestions do you have for starting to check the most common problems?
Thank you for help.

Water pump or thermostat most likely.

Does it overheat while idling or driving/

Thank you for help. It seems to do it when driving. Actually it is confusing to me: we put in some antifreeze and car was running fine and not overheating the first time used and we thought that we solved it. The second time uded, within couple miles started overheating and went rpidly to the red line and had to be turned off.

May I ask: if we turn it on and let it just idle and it overheats: would that be a different problem?

Does it overheat while idling or driving/

It would heat up at a much more slowly pace. It sounds like your water pump is bad. After about a mile its to hot to drive. Ide replace your thermostat as well.