This is because of a modification to BlockWater they make which reverts this:
https://github.com/CoFH/CoFHCore/blob/master/src/main/java/cofh/asmhooks/block/BlockWater.java

To fix this I can:

1. Use ASM
2. Check for PlayerInteractEvent and revert CofhCore's reversion

I'll probably go with 1 but it has not been implemented yet