Add bubbles and straw
On another layer, create 2 or 3 bubbles and add them to a group called bubbles. Duplicate the water mesh, scale it just a little and add a particles system. Set Type as Hair and Emit From Faces. In the render tab of the particles system, deselect Emitters and add the bubbles group. Now add a circle ( with 8 vertices) and extrude along the Z axis. Add some Loop Cut and set Subdivision Surface to level 2 and solidify modifier. In Object mode, set shading as smooth and put it inside the glass.
Adding the bubbles
Add a plane as in the image below, enter Edit mode and Unwrap. In Object mode, add a new diffuse material and then add a floor texture in the Texture tab. Come back into material tab, click on the T button (at the right of the reflectance color) and select the floor texture. Select the glass and add a dielectric material: set interior IOR as 1.49 and exterior as 1.00. Select the water, add another dielectric material (interior IOR 1.49 and exterior 1.33 ? and be sure that the Normals are oriented the same as the image below).
Enter interior IOR 1.33 and exterior 1.00 for the top of the water, and interior IOR 1.00, exterior 1.49 for the bubbles. Select the straw and add a white plastic material, then add a red plastic material and (in Edit mode) assign it to the right faces.
The material settings
Scene and render settings
For this render we'll use a photon mapping integrator, which works better in a closed room, so add some planes (assign diffuse material) around the scene as in the image below, set the camera and add a sphere inside the scene (emission material).
In the render tab choose Photon Mapper
and press F12 to start the render. If the result is too noisy try to increase the photon number and/or samples (in my work I used 96 pixels-per-samples).
Top tip: Post-production with Gimp
Open the image with Gimp, adjust the curves then duplicate the layer. Add a Gaussian blur (20-pixels) on the new layer and set blend mode to ADD.
Post-production with Gimp
Check out Filippo's website
To follow Filippo's tutorials, you can download the open source software Blender