The problem I see with leaving the water is this.
A few years ago, a nieghbor had a kiddie wadding pool, with a clear
bottom, in the yard, in the 90 deg FL weather. When he moved it, the
grass under it was the only grass on his property! The heat, without
rain, causes the lawns to brown out. The pool, with water in it kept
the grass (and soil) under it cooler.
I wonder how much a bunch of 1" long knife cuts would let heat escape?