Spoon Sports 10/13/2011"We hired a van" - I doubt it.
"Am I thinking right that owner forgot to fill the water/coolant before we set off" - Even he filled it to the brim, there was HOLE so it doesnt matter, the problem is the hole.
It can be that the hole happened during your trip. Does the radiator look like its been through hell and back? Where is the hole at? what area? That can tell a lot on what has happened or how it happened.
Sorry but im online, things are a lot easier seein it in person.