The alchemy jug is a common magical item found in many fantasy role-playing games.
This jug may be any container that holds liquid, it could be a jar or a beer mug, or even a canteen. They all have one thing in common though. The ability to pour out various liquids. This jug can be used up to seven times per day, but only one type of liquid per day may be poured.
It is capable of pouring salt water, fresh water, beer, vinegar, wine, ammonia, oil, aqua regia, alcohol, chlorine, and cyanide. The exact amount created depends on the liquid, with salt water being up to 16 gallons, while cyanide is a mere ½ oz, with other liquids being in the middle.
This jug is particularly of value to those who live in desert cultures, because it can produce up to 56 gallons of fresh water per day. Or 28 gallons of beer, which would be even better.
This is only my interpretation of this item, which is based largely upon its use in the older versions of the Dungeons & Dragons series of games. Your alchemy jug may only spew out Diet Pepsi, molybdenum disulfide, and motor oil. To be totally safe, you should read the instructions.