Whenever a Bubble Column is created, either with a magma block or soul sand, a source water block gets created at the highest flowing water block, creating another from the highest point until the source gets drained and the block creating the bubble column gets destroyed. But the water source created from the bubble column would still be there after draining it and would manually have to get removed

Apologies if what I said is confusing, but to sum it up, bubble columns creates new water source blocks from the highest flowing water block and