Water stream bending to electrostatic charge Why does the water stream really bend towards a charged comb?
I share an hypothesis that the 1000's of YouTube videos and similar number of scientific and scholastic articles presented as proof of the polar molecule attraction to a charged comb is incorrect.
The usual experiment shown is a thin stream of water from a pipette or faucet being attracted toward a charged pipe, comb or balloon. Then the comments follow that tell the observer that they have witnessed the hydrogen ends of the water molecules all being aligned toward the charged comb thus causing the bending.
I admit I got the idea of this explanation being wrong from an article entitled:
Electrical Deflection of Polar Liquid Streams: A Misunderstood Demonstration
Journal of Chemical Education • Vol. 77 No. 11 November 2000 • JChemEd.chem.wisc.edu
The authors state," Intuition suggests that any nonuniformity in the electric field near a charged rod a few centimeters in diameter, or an electrified balloon, must be far too small to have any detectable effect on molecular dipoles."
I agree.
In one video, the presentor claimed to prove his case for water molecule covalent polar status being the reason for the bending of the water stream by next demonstrating that a stream of toulene, being non-polar, did not bend. But I note that toulene, with 15 atoms, is heavier than water with 3 atoms.
I welcome any thoughts. I find that my source is widely quoted, but there are all those school kids who may be seeing an incorrect assumption every day.
This polar attraction demonstration either needs proof or the other hypotheses of ions or fields causing this attraction need to be studied.
 A: From the paper:

Dipolar  entities  can  only undergo  deflection  in  a  nonuniform  electric  field  whose strength varies significantly on the length scale of the dipole.

... and so does a magnetic dipole in the inhomogeneous field of another magnetic dipole. The necessity for an inhomogeneous field does not sound like a terribly nasty limitation, otherwise permanent magnets couldn't attract each other either.

Intuition suggests that any nonuniformity in the electric field near  a  charged  rod  a  few  centimeters  in  diameter,  or  an electrified balloon, must be far too small to have any detectable effect on molecular dipoles.

Wherever the author's "intuition" comes from, mine does not seem so easily suggestible. Why isn't a "magnetized" solenoid a few centimeters in diameter far too small to attract a piece of iron? Electric permittivity of water is around 80, magnetic permeability of iron starts at around 300, so no orders of magnitude inbetween. The dependency on distance is the same for magnetic and electric dipole attraction. Also note, that the balloon is charged, so it is even an electric monopole attracting electric dipoles.

In fact, the explanation for electrical deflection of a polar liquid droplet stream is that the polar liquid droplets carry an induced electrical charge.

The facts are, polarization of a droplet in an external electric field amounts to an effective surface charge on one side of the droplet and an opposite surface charge on the other side. That's what I would call an induced charge. The surface charge closer to the source of an inhomogeneous field will dominate the resulting force due to the $1/r^3$-law of dipole attraction. What happens to the surface charge on the other side of the droplet is practically irrelevant, especially whether the charge has stuck to the outlet of the tap, or if it is still on the droplet.
If the droplet were a conductor, the surface charges would even be more, but hey, at least its highly dielectric water with permanent dipoles that can align with an external field, instead of some nonpolar stuff which has to rely on van-der-waals forces for its permittivity.
Who cares if the author has done some other experiments where some charges are demonstrably transferred to the outlet, and they work for homogeneous fields as well. This is comparing apples and oranges.
What the author fails to show is the proof of the elementary conjecture, that the forces between the induced/aligned electric dipoles inside a water droplet and a locally charged and isolating balloon cannot possibly deflect a droplet. Instead he refers to a nebulous "intuition".
I would say, if a charged balloon can pull non-polar hair up against gravity, it can easily deflect a highly polarizable water jet. Until proof of the contrary.
A: The website at the bottom talks about ions in water.
"Water, even pure water, has an amphiprotic nature. This means that a small amount of ions will form in pure water. Some molecules of H2O will act as acids, each donating a proton to a corresponding H2O molecule that acts as a base. Thus, the proton-donating molecule becomes a hydroxide ion, OH-, while the proton-accepting molecule becomes a hydronium ion, H3O+."
So, if you are correct that the polarised molecule reason is incorrect, then perhaps this is an alternative explanation, just an idea and it would be interesting to see others.
The ions in water would be moved one way and oppositely charged ions would move in the opposite direction. Then there could be a net attraction to the balloon or comb.
The water stream wouldn't break due to surface tension, so it bends.
See also https://en.wikipedia.org/wiki/Self-ionization_of_water
https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Acids_and_Bases/Acids_and_Bases_in_Aqueous_Solutions/Water_Autoionization#:~:text=Water%2C%20even%20pure%20water%2C%20has,will%20form%20in%20pure%20water.&text=Thus%2C%20the%20proton%2Ddonating%20molecule,ion%2C%20H3O%2B.
