Note Updated version as of 22nd Jan 2016:
I have been busy creating the next generation diverter.
Inspired by a couple of these devices seen on Thingiverse.
This one fits a tap aerator with a diameter of 23.5mm.
What makes this different is the annular manifold at the top which helps prevent the aerator choking and keeps it working smoothly to allow a steady aerated stream.
Simply placing your finger over the bottom opening gives nice bubbler style water flow from the top to rinse your mouth or drink.
UPD: I printed another in clear ABS, needed to increase the scale by 2% in the printer software, would have been better 3% in hind sight.
The Silver version was made in PLA, I think items that are going to be in contact with water are better in ABS. PLA can slowly dissolve while PLA is safe I do not know what the colouring agent is, that might leach out and cause a problem, clear ABS should be fine.
I printed this in PLA with standard setting of 3 layers top, bottom and perimeter. I used a 60% fill and it worked fine.
I do have concerns about PLA being in contact with water and I will make this in ABS in the near future.