The water injection could indeed be helpful, but remember that there’s a huge difference between water injected (atomised) and water droplets.
Anyway as someone said in the topic Monstro linked to, water droplets, being heavier than air, just don’t follow the curvature of the airflow, and they simply end on the back side of the airbox without entering in the trumpets.
Unfortunately with sand the engine isn’t so lucky...
