Hiya, Joan,
You can get a bottle of something called Radseal from Halfords to pour in...this circulates around and plugs the hole when it find it. Sometimes works, not every time...depends on how big the hole is. Are you sure it's not leaking out of a hose connection that's worked loose? Water will sometimes appear quite a way from where it's actually leaking. A mechanic friend of mine who's beenin the car business for many, many years, swore by putting a raw egg in the radiator (yes, not joking!). Again, sometimes works, not every time. Your problem will get worse when you come to put antifreeze in if you really have got a small hole, as antifreeze will always find a hole where none existed before! I've managed before to buy some Chemical Metal from Halfords to make a seal over the hole, but you've got to clean around the hole making sure it's dry before the stuff sticks. Bit difficult if the hole's in an inaccessible place. Only safe bet is to have it looked at. May just mean a garage welding or brazing a small patch over the hole. I would get it done now rather than later with winter here.
Hope all this helps. Best of luck!
Denis (CarAid mobile repairer)
Denis Langley, November 2007