Even the smallest containers of water are helpful to wildlife. There are no limits.
A container just a couple of inches is deep is sufficient for frogs to lay spawn.
A small basin of water, kept ice free during the day, is useful to birds in Winter.
I have an upturned dustbin lid in a depression on the the ground, containing a few stones and water, which is used by birds and small animals.
If you were to use a washing up bowl, then I'd include a big stone, in the bowl at the side, so that small animals could get in and out easily. And birds could stand on the stone, to drink and wash.