Llama spit disappears when it hits either flowing or source water as though they were solid blocks. In the image below the white cubes are markers of where the llama spit has been.

Steps to reproduce:
  1. Put llama in minecart.
  2. Put wolf in minecart.
  3. Put water imbetween. Turn on f3+b so you can see the actual llama spit entity through the particles.
  4. Llama spit does not hit the wolf, and you can see that it does not go through the water.
  5. Remove water.
  6. Llama spit now hits the wolf.