In combination with a Compressor, it will automatically extract the Water with no need to use an Empty Cell. The Compressor will then produce a snow ball out of it. This can be extremely useful to cool down a Nuclear Reactor as snow balls can be compressed again into ice blocks. This will not work with a Singularity Compressor, though.
To pump water into empty cells, place them into the top slot of the pump. To pump water into empty buckets, you need to put them in an adjacent normal or double chest. Alchemical chests, condensers, chests from the Iron Chests mod (e.g. diamond chests) will NOT work with empty buckets.
Maximum input : 32 EU/t Before Exploding