I fail to see the problem. We are both factoring out gravity. Without the force of gravity the water travels in a straight line.
Somebody doesn't seem to know what a frame of reference is!
I agreed with you that according to the revolving sources frame of reference the water appears to curve. You already agreed that measured against a stationary reference the water travels in a straight line. I am not disagreeing with you.
"I fail to see the problem. We are both factoring out gravity. Without the force of gravity the water travels in a straight line." [excerpt, bold emphasis mine]