Even for just flower water, I would avoid an inappropriate volume. An unventilated standing puddle will not be a source of joy.
Ok, that was just an idea anyway.
What would be an appropriate volume for about 300m² of planted garden area?
You can even rent running ducks during snail and mosquito season. Dragonflies that settled by the pond helped us against mosquitoes. They are pretty and have adequate food at the same time.
Ah, thanks, I'll remember that!