The fluid began streaking across the top of the aileron after takeoff began just before rotation, was a lot of fluid, enough to leave a vapor trail from takeoff until cruising alt. I wasn't able to get a good picture of the vapor trail, it was hard to get it to contrast against clouds. At one point it was flowing across the entire aileron. The last time I can remember seeing fluid coming from their aircraft was on their 732's which is common on those engines, this was definitely in a much higher quantity. We were delayed for mech. for about 20 minutes before takeoff but apparently everything checked out.
I asked a FA in passing and she mentioned it was probably water. Just before descent, looked out and the fluid was still coming out 3 hours later, still leaving a vapor trail. Buddy of mine was in 17a so I took a look out that window and no vapor on the LH side. Hard for me to imagine enough water building up to still be flowing 3 hours later, at least in quantities enough to leave a vapor trail. After deplaning I saw a small puddle underneath the outside of the wing.