My initial strategy was to use 1 of each input to construct a third of the product, and repeat 3 times for each output.  But I struggled for a long time to find a geometry that allowed the inputs to coordinate well, and ultimately failed. 

The key idea that helped me unlock 39 was realizing that the inputs actually did not have to coordinate.  If I placed a debonder one move from the 3-stick, I could treat the water-end of it just like a single-atom input with 1 extra latency.  That massively relaxed the requirements for how the true single-atom input could be placed, and meant that all of the water molecules could stay towards the outside of the workspace--no need to cross over.

You can see this in the solve if you look closely.  The 3-stick water atoms are used on one half of the input, and the singletons on the other half.  Every product third uses a different combination of water atoms.

******

Sidenote: I kinda wanted to leave this one at 420G.  Oh well.  Business before pleasure.