...
By observing the water jet at different flow rates it was determined that the length of the jet is dependent on the velocity of the jet. At low flow rates the length of the jet is shorter than at higher flow rates. The length of the jet refers to the part of the jet where the water surface is turbulence-free and thus appears smooth and transparent. It is when the surface of the jet becomes sufficiently turbulent that air is entrained as the symmetry of the jet breaks during free fall. When a jet hits the water surface a void forms in the water and from the tip of this void an air bubble is pinched off as demonstrated in the attached scientific paper: The entrainment of air by water jet impinging on a free surface by Wee King Soh et al.
Therefore, when the water jet hit a solid smooth surface there was no foam formation.
...