Drip watering greenhouse

I have some stuff I can use for a drip watering including a large header tank. Would it be better to locate this inside the greenhouse and feed it with clean tap water or put it outside and feed it with rain water.

Im guessing inside with tap water but thought I better check.

Outside, you want all the indoor space for the important stuff, plants.

I'm paranoid about blight - very paranoid. Its an old CH header tank (42gal) so Id only be loosing 1ft of bed width which I can easily box in and put a pot on top  Id rather drop 1 plant out than kill everything in their with blighted water.