Swimming in normal water
You might want to try fiddling around with the fog values within the .vtf and make the fog end a much larger number.
i fiddled like the pied piper and I aint got nothing close to the desired effect. I was hoping someone would copy and paste THEIR values for such similair water
Is it even possible to have fog effects in a moving water volume? This page seems to indicate it isn't.
Other Portal 2 maps: Medusa Glare
Portal 1 maps: Try Anything Twice | Manic Mechanic
Then how did they do it for the sludgey goo textures?
Are you creating waterfalls? That needs so different materials! And not the func_water_analog entity but func_brushes textured with scrolling textures 
Really, can you please explain what exactly are you attempting to make?
useful tools and stuff here on TWP 
[spoiler]
[/spoiler]Why would they even be included in the portal 2 water .vmt's at all then? Puzzling!
You can tie a seperated fog_volume to your moving water. I was working on something like that the other day. I'm a bit busy rght now, I'll see if I can post what I did later.
Edit:
It's nothing special actually. Just a fog_volume the same size as the fully "opened" moving water. And a trigger_multiple slightly under the surface (so it doesn't get triggered when the player touches the water but his view is still above it) parented to the moving water to toggle the fog effect. It'll probably not look as fancy as a normal _underneath texture, but it's at least something.
Are you creating waterfalls? That needs so different materials! And not the func_water_analog entity but func_brushes textured with scrolling textures
Really, can you please explain what exactly are you attempting to make?
The waterfall is separate from the water, It is activated by turning a valve and it comes flowing flowing from a spout near the ceiling and causes the water to rise in this room so the player can reach a higher level of the map. I currently have the erase gel as a substitiute for this water coming from the spout. It is not a good fit cause when you are underwater, you feel like you're just in zero gravity
the fog volume doesn't really seem necessary with a trigger involved. But it finally got the desired effect. thanks
Ask HMW if you can borrow the waterfall area from A Beam Too Far?
the search engine keeps giving me a general error when I look for that guy and his map. I think it has a 4 digit minimum search protocal or something