Faucets

When creating Blue Portals, the developers wanted to take the Source Engine to the next level. To do so, they brought in a "fakenamic" water particle, created by a member of the Garry's Mod community called Facepunch (with permission). The new concept was using the fakenamic water to to tasks such as turning a water wheel to open a door, or to keep the player from putting the Fire Cube in a certain area. This concept is first seen in the first High Interest Chamber (06 in the first Blue Portals).