It used be thought that the cold water allowed fast fills by keeping the gas cold too. Tests and calculations show this is a minor positive effect, whereas water in your cylinder is a major negative effect. Good fill stations don't do this.
Except that it works.
I’ve been having my tanks frequently filled this way for 5 years now. It makes a difference.
The shop I use most often uses a cold water bath. They come out cold to the touch & are at 3600-3800 once they warm up. I’ve never had them get water in my tanks. The shop turns my tanks around typically in 20-30 min. 1000 psi to 3600 psi in 20 min consistently. I’ll take it.