[sikonomial]

It shouldn't be too difficult to fill up a balloon like container at the bottom of the sea with fresh water. Once the container is filled it will float up to the surface.

The container doesn't need to be super engineered, since it is filled with water so there is no pressure difference between the inside and outside.

[solatic]

If you have balloon-like containers instead of a pipe, then you expend energy to submerge replacement containers down to the depth at which desalination happens.

[sikonomial]

You can just have the container be slightly more dense than water and it will just sink.

I guess many people have not been scuba diving since these concepts seem so foreign to them.