Here is the reply from 3M US engineering team

Carbon Block used in APDWS1000 is acid washed wood based carbon. The acid is used to help clear the pores of ash during the activation process. The initial draw of water with a silky/soapy consistency might have an elevated pH due to the alkaline cleanser used to neutralize the acid residual.

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Added on October 18, 2012, 6:43 amAnother thing to add on, some forumers saw the word soapy, they thought it is like soap. FYI, the water is smooth/silky initially due to alkaline as explained by 3M and it is safe to drink. Just need to flush approximately 10 min before using