When you're out of water, everything works fine. Except that this is the aquatic update, so let's go underwater.

I think there was a snapshot in which it was possible to pick up the water from a waterlogged block instead of the nearest water block, by holding the "Sneak" key. I might be wrong about that, but either way, this is something that is necessary. Not only it would come in handy (and quite a lot), but it would also... I mean, for some blocks, it would otherwise just be impossible to remove the water, unless pushing ourselves within it (with a piston) or removing all the surrounding water (well, there's still the bug that creates water sources on waterloggable blocks anyway, but let's imagine it's fixed).

Those blocks, or at least the ones I noticed, are the following :

You can't pick the water from the chest or the cobblestone wall (but you can on fences), whatever you do. It's the same for stairs and slabs, but only in some cases such as the one shown in the screenshot.