Heeeeeeeeelllllllllpppppp

Has anyone ever come across this before, you drive your Cossie day in day out no worries, no signs of water leaks or head gasket problems, you park it in the garage after a day out then 1 2 3 4 5 hours go by and all of a sudden it starts dropping its water from somewhere around the engine area but no sign of from where

Last night I went out hour after hour and nothing, then when she was stone cold after about 5 hours of not running out comes its water but never when im watching and as stupid as it sounds no sign of from where!

Any ideas guys

Cheers Jase