When you set-up your autoclave together with the Enbio Magic Filter, you will need only 1 water container.  Remember that the purpose of using the Enbio Magic Filter is to purify and recycle the water used in each sterilization cycle, so that we can use it again. Hence, 1 liter of water can last up to 1000 cycles. If you set-up your autoclave without the Enbio Magic Filter, then you will need 2 water containers. One should be empty (for the waste water) and the other should be full with demineralized or distilled water.