But reported cases of lowering water tables, ecosystem damages, saline intrusion, stream depletion, and land subsidence observed in some of the most important OECD agricultural regions provide evidence of highly damaging external effects that call for policy responses. Lack of information on groundwater resources is bound to lead to an inability to identify and adequately treat groundwater problems. Information collection is costly and needs to respond to a demand, but insufficient investment in groundwater information and data will prevent effective management.