Mine was the waterpump.
Easiest way to see if its leaking is honestly just to whip the tray off and start it up, put a breaker bar or jack handle jammed between the seat and the accelerator so it revs around 2500 and look underneath. Bottom of the radiaters a weak point, waterpump and any of the hoses to and from the EGR cooler, if no drips then its either the head or the internals of the EGR cooler have broken down and allowing water into the engine where its being burnt off, you will know if its the EGR cooler as when you start it from cold it will either stall or run like a sack of sh*t for 30 seconds while it burns the coolant off thats leaked on top of the pistons while its been sat from the previous time it was used :)
f*cked cooler -
f*cked head -