A second-generation hydrogen bond donor (HBD) anion receptor with an inner amide cavity and an outer urea cavity can selectively and efficiently extract arsenate (AsO43-) from water in the presence of competitive oxoanions and halides. The X-ray structure showed encapsulation of AsO43- in a π-stacked dimeric capsular assembly of the receptor, the first crystallography-based example of pentavalent AsO43- trianion recognition by a HBD receptor.