Get some proper coolant in ASAP; the aluminium radiator will be quickly damaged if you leave plain water in there, and then you'll have another leak and another problem.
Some say even leaving the radiator empty but wet for 48hrs is enough to cause significant corrosion damage; the advice if storing one is to dry it internally using compressed air (or whatever; hairdryer perhaps?) before putting it away.
Really? thats bizarre considering aluminium is very unreactive with water.
I have enough coolant to fill it once haha, so I put water in first to run & check for no leaks