Board Thread:LotR Mod Technical Support/@comment-29810282-20171113214033/@comment-31507215-20171113224036

That is because the mod is in version 1.7.10. The ability to fill buckets from full cauldrons was added in 1.9.

On most pages on the Minecraft Wiki, you can look at the History section to see when a certain mechanic is added. If it says it was added in an update after 1.7.10, then (unless Mevans has added it himself) you won't be able to do it in the mod.

Hopefully that helps!