In versions of Minecraft before 1.21, any waterloggable block generated onto an existing water source block as part of a structure would be waterlogged, with no option to change the behavior. This works fine for underwater structures (eg. shipwrecks) but is horrible for something like an underwater dome, unless the structure foregoes using any waterloggable blocks.

1.21 fixed this by adding a liquid_settings option to structure definitions, but it would be nice to have an equivalent feature for older MC versions.