All water is not at the same height everywhere here on Earth.
Although water does tend to find it's own level in a connected system, the global sea level does vary due to factors such as Earth's rotation, gravity as well as density variations.
Also the local sea level changes as a result of factors like currents and tides as well as global warming.
The Earth's gravity is not perfectly uniform, and it's uneven distribution also affects how the water is pulled and causes variations in sea level across the globe.
And the Earth's rotation or spin also creates a centrifugal force, which is strongest at the equator, and affects the distribution of water and causes the water to bulge slightly at the equator.
And variations in the density and density differences of the Earth's crust and mantle also influence the gravitational pull and consequently sea level.
Other factors in the waters height are Tides, currents and Eustatic changes.
Tides are caused by the gravitational pull of the sun and moo, which creates bulges of water that move around the globe and cause sea levels to rise and fall locally.
Ocean currents also influence the sea level by moving the water from one place to another.
And eustatic changes which are global changes in sea level, which are often caused by melting ice caps or thermal expansion of water as a result of warming temperatures.
Although the variations exist, the differences in the sea level are often small when compared to the overall size of the ocean.