What do you put in the cooling system of a 1993 ford explorer can you put water instead of coolant?

I would only put water in an emergency situation where I don't have coolant available. The coolant helps the engine to not overheat and to not freezing, while that could happen if you just use water. If you don't have your vehicle's manual to know the specification of the coolant, you can use the generally available Prestone and add water according to the table on the coolant's recipient. (or you can buy the pre-mixed formula)