Underwater with air?

I recently stumbled upon this video on YouTube

Does anybody know how this person did this? The physics of water aren’t even there like how you slowly fall down.

Life support addon. The climate regulator or gravity plating can achieve this.

facepalm…erm I mean facepunch lol I don’t know how I didn’t think of this. I’ve used LS before

Wow, I never knew Life Support could do that. I’m redownloading it.

this isnt life support, he made everything in the source SDK. the Water in the source engine is not dynamic its static.