Many/most (?) swimming pools (at least where I live) have autofillers. They work essentially like the plunger if a toilet. It could be nice if a Rachio zone could be used to control an autofiller though this setup would need to be somewhat unique in that "it" (the mechanical side of it in the pool) would need to be able to signal Rachio to turn off. On the Rachio side, with respect to turning it on, there could be separate schedule that runs every few days.
Just initial thoughts - maybe it's actually a very stupid idea.