leak on my 52 plate vectra elite?

i have a puzzling problem with my 52 plate vectra elite when i am sat ticking over at lights or something i have water dripping from a little outlet pipe under the bonnet it is at the back of the engine compartment but it does not smell of coolant , fuel or screenwash it just feels and smells like clean water (like rain water) my fluid levels do not seem to change i don,t know what it is can anyone help