For studying these interactions at the molecular level, clusters of water as well as ionwater clusters present ideal model systems . In the past decades, such clusters have been investigated both spectroscopically (see, e.g., Refs. as well as computationally (for reviews, see, e.g., Ref. ). Despite increasing computational resources as well as methodological advances, the accurate, yet sufficiently efficient quantum-chemical treatment of large molecular clusters remains a challenging task.