Semi Water Physics?

I have seen a video on youtube in which water would pour from taps down over some object, And then would flow over the object, And you could also drop the props in different positions, and they would still have the “Semi Water Physics”

How do i do such a thing?

I think you are referring to info_particle_system. Atleast you can use it in L4D I dunno about other OB games though, but the particle effect name for L4D is rain_stream_01, rain_stream_02 or rain_stream_04.

Cool, Thanks