Sponges in Minecraft Pocket Edition have always been kind of pointless. At least compared to Minecraft for PC where they can be used to soak up the water around it. The Useful Sponges mod makes it so that when the block is placed down it will remove the water around it.
How does it work?
Do you need to drain your swimming pool so that you can clean it? No worries. Just place down a sponge block in the center of the pool and it will soak up most of the water.
- Sponge (ID: 19) – 1 water bucket + 1 yellow wool
You can similarly use the sponge block to dry up entire rivers.
Even large oceans and lakes can be dried up using this technique of water draining, but it would of course require lots of sponges!