The way i imagined it:
The surface of the pipe interacts with the water-surface passing it in a way that makes that passing easier, it won't have much of an effect on the fluidity of the water not touching the pipe, merely negate any 'stickyness' within the pipe.
So the moment it leaves the pipe it would lose any benefit.
For the pipe to have a lasting effect on the fluidity of the water:
- It would have to leave a substance in it, in which case the pipe will slowly dissolve or the active ingredient needs to be replenished requiring the pipe to be disassembled.
- Or it could catalyse a change in a substance solved into the water but that would have to be an addition to the water before it enters the pipe because none of the normally occuring substances in water can be catalysed into watertension reducers afaik.
I didn't think of the low turbulence design, interesting idea.