Witch Water is made by putting a barrel on top of or adjacent to a block of Mycelium and filling it with water. If you already have water in a barrel and you put Mycelium around it, you have to take the water out, and put it back in the barrel. Edit
- If you fill a barrel with Witch Water and right click with sand, it will turn into Soul Sand (This process can be automated with hoppers)
- If a mob falls into witch water it will continuously take damage except for Zombies and Witches
- If a Creeper falls in it, it will become a Charged Creeper
- If a Pig falls in it, it will become a Zombie Pigman
- If a Skeleton falls in it, it will become a Wither Skeleton
- If a Squid falls in it, it will become a Ghast
- If a Spider falls in it, will become a Cave Spider
- If a Villager falls in it, it will become a Zombie Villager
- If a Villager Priest falls in it, it will become a Witch
- If a Luggage falls in it, it will become supercharged (doubles inventory slots)
- Witch Water can be exploited in the Nether as it behaves like water without evaporating,
Notable conflict with another mod: B0bGary's Obsidian Tools 
- When smelting Obsidian chunks in a furnace, the end result will be source blocks of Witch Water instead of Obsidian ingots. This conflict currently exists as of the V1.28 of Ex Nihilo. This is because the Witch Water block's ID is the same as the Obsidian Ingot's. The ID can be changed in the config.
- You can make infinite Buildcraft energy by making a Wither Skeleton farm and utilizing the coal they drop.
- Witch Water, and the soul sand you get by combining it with sand, is the easiest method of making a nether wart farm, as the nether wart will occasionally drop from a sieved soul sand
- You can create Ghasts with more ease by putting a waterfall next to a pool of Witch Water so that squids that spawn fall into it.
You can create Rose Bushes by placing a Poppy in Witch Water.
You can create Sunflowers by placing a Dandelion in Witch Water