Believe it or not, when water finds its level, it does not form a straight line. Because the Earth is curved, and gravity pulls in objects from all directions, water will be affected by these, and since water can’t be perfectly level unless all sides of it are being equally affected by gravity, bodies of water will always have a curve to them. Based on the area that the water takes up, that curve may be indistinguishable from a straight line (a glass of level water is considered straight, but the oceans are not).
Now, some of the skeptics may be saying “gosh, well what about the oceans? They are curved, but they can’t be level because they are always making waves, which means that there is an unequal pull on them as a whole! ” Well, you’re not wrong…
If the sun and moon didn’t exist. Because the moon is so close to the Earth, and the sun is so massive, they have slight gravitational affection to the Earth’s tides, causing waves, and an unequal distance from the top of the high waves, and the top of the lower waves, from the center of Earth’s gravitational pull. Take out these two forces (and any others from other planets), and the tides would be perfectly still, meaning they would be level.
So really, you can’t actually ask this question and get any reasonable answer. Water’s level is dependent on the shape of Earth’s gravitational field,
