I assume you have a fresh water holding tank so you must have a fill cap for it, the water heater is also connected to the fresh water tank hopefully..
I could be wrong, probably am, but that doesn't look like a fresh break.. it may have been cracked for a while.. fixing it is beyond me but thanks for the picture and it may help...
That looks like no pick-up tube I've ever seen.. looks like a pipe plug. In any case hold the large fitting with an open end wrench and then remove the small square fitting..