Bypass exists by placing bucket on waterlogged blocks like half slab, trap door, etc.

[msudol]

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Waterlogging introduced in Minecraft 1.13 allows some blocks to hold water, since PwnBuckets places the source momentarily and then sets it to running water to get the flow effect, the block becomes waterlogged and therefor, holds the water.. and source pool can be made in this way.

Waterlogged - Spigot API