If the water stays in the bucket then you must admit that water doesn't always find its level downward. You must also admit that water can be acted on by forces other than pressure, as you conveniently forgot to mention in your post. In this example the water finds its level in the direction of acceleration (the bottom of the bucket).

If water can be acted on by acceleration is it such a leap to accept that all the water on earth that is apparently level, is being accelerated downward by some force?

If you visualize a sphere with the direction of acceleration toward its center, instead of outward like the bucket, you can visualize a how water could bend around a sphere.

If you can't complete this simple thought experiment you may be too afraid to trust yourself.