Some questions ;]
How to create water?
How to create working info_overlays(http://img685.imageshack.us/img685/2246/64151517.png)?
They have a good writeup on how to create the water hazard. I have a few projects with working overlays, so I'll go take a look at what I did to make them work the way I wanted
It is probably made with texture_toggle and logic_relay?
The Valve Developer Wiki has a full tutorial for creating working indicator lights for Portal 1.
http://developer.valvesoftware.com/wiki ... tor_lights
Perhaps I'm putting my foot in my mouth here since I haven't created these in Portal 2 yet, but I believe the process should be pretty much the same?
(What I didn't understand was how env_texturetoggle worked; I kept looking for a place to setup exactly what textures I wanted to swap between, but as it turned out the indicator light textures are simply magic and just happen to understand the SetTextureIndex thingy.)
Remmiz wrote:
I believe they are basically animated textures that don't play. When you use the SetTextureIndex you are just changing it to that frame in the animation.
Ah that's interesting. How do you know if a texture supports animations or not? Can you tell from the texture browser?
http://img801.imageshack.us/img801/4619/17073533.png
http://img36.imageshack.us/img36/6665/79433575.png
maybe cubemaps need?
i try with cubemaps, don't work too 
Cubemaps are for making things be properly reflective and shiny in response to the light on your map. Whatever problem you're having, it's a general Hammer/Source issue, not Portal specific.
If you're using a sign (X that changes to a check), then use prop_indicator_panel. you can set the linked indicators, and set your triggers to "Check" for the panel. When its triggered, it will change the panel and all of the indicators.

here images:
http://img189.imageshack.us/i/47853227.png/
http://img850.imageshack.us/i/39985807.png/
maybe my Hammer has broken?