Every setting needs to think about why the islands are floating. Even if the whole POINT is that it's magic and there is no "why", you still have to figure out why, because it is a thing that players will interact with and you need to be able to make it behave consistently.
That said, those reasons can be varied and complex, and you should keep that in mind when you claim that something is inconsistent.
The ponds aren't always full, but when it rains hard it takes a little while for them to fully drain out (especially if some of the land masses are made of soil instead of rock, they would hold water like a sponge and slowly drip out the bottom) and that's when you see the waterfalls.
-The islands are so high that they collect vapor (especially in the morning), which runs off of them as liquid water, and then turns back into clouds before it hits the ground.
-Some islands magically create water and are responsible for rainforests far below them.
-Some islands intersect with polydimensional waterways (just like magically creating water except that the ponds are portals and might actually lead somewhere)
-Yes, the islands can theoretically hold infinite weight, they don't suspend gravity but they do magically counteract it in such a way that weight isn't a factor, that's how you get tons and tons of flying rock in the first place.
-No, they don't hold infinite weight. That tiny island with the huge tower was floating a lot higher in the atmosphere before the tower was built, but he did the math and knew it wasn't enough weight to crash it.
-The islands don't float at ally, they're anchored to their place in the sky. Specific mineral deposits act as the anchor, the rest of the island slowly crumbles away over time, so the smallest islands are actually the most stable because they've been reduced to just the anchor-mineral.
-You can't mine the mineral, it's immovable (or, you can, and that's what immovable rods are made out of).