Well, I don't think anyone simulates with a realistic number of molecules. The least realistic fluid animations use a particle emitter, where the particles use a 'blobby' algorithm to simulate a fluid surface. A single particle looks like a polygon-sphere, a droplet. A tight line of particles looks almost like a true fluid stream. The major downfall is that the particles don't have any expression of 'surface tension' or volume, so they freely scatter and also can flow to a single small spot. Scriptable particles have partially overcome even that drawback, if you can script in a kind of attraction that has a min. standoff distance, and still incorporates friction between objects, damping, and so on.
True fluid simulators that do all the work internally still operate on a mesh that you produce which has a relatively small number of vertices. Just like Finite Element Analysis (FEA) used to simulate the failure of a given part design that uses a given material, such as acrylic plastic or a certain aluminum alloy. The part model, usually created in software like Solidworks, is broken up into elements, small blocks, so that the part looks like it is made of tiles, like the space shuttle. (It also has a resemblance to a quad-only polygonal model where all the quads are the same square area.) But the tiles are blocks, and the entire solid has been 'blockified'. Then the expected 'force' is applied to the part in a specified vector, and based on the material selected, an analysis is performed and a report is produced that details the amount of force that produces deflection and ultimately failure of the part. Usually an image is generated that shows which areas of the part are stressed the most, allowing the designer to rework it to improve his design.
The point is that these sims usually work on mere hundreds of elements, maybe several thousand at the most, not tens of thousands, and certainly not millions. You might be able to make something that looks like flowing sand or wheat, or maybe even 'like' a fluid, if some more advanced physics scripting is added. But since SU doesn't do any special rendering, the best is could probably look like is 'watery particles'.
