Is there a way to render one layer So I'm creating a room flooding video I've taken a picture of my room and and created a scene that has obstacles where my bed is and the walls are ect. What I want to do is render the fluid simulation against a transparent background so I can composite it on to the picture. The problem is I can't figure out how to make all the obstacles invisible and only have the fluid running through the scene and hitting the obstacles without the hdr making the fluid over exposed.
Yes, there is. In the properties panel ( to the right ) hit the button in the top bar next to the render setting (next to the camera) which looks like two pages. This is called the Scene settings. Under layer, you can choose which layer to render. Hope that helps :). 

Edit: There is one more thing you can try. In the top right where it shows the different objects in the scene, you can’t hit the camera so they won’t be visible in the render. I’m not sure if this will preserve lighting though.