Water pipe leak help?!

[Jon.L]

ive noticed some steam slowly coing from under my bonnet wen im stationary, checked the coolent bottle sure enough not much left! now im pretty sure what pipe it is but i want to make sure, is there only the one pip that slips into two at the bottom to join the radiator, its a Y shape? is this the only possibilty?

 

[caister]

Could be leaking from the thermostat housing.