Spain and Greece (right panel) have also increased their use significantly, if at a less steady pace. Japan has significantly reduced its agricultural groundwater use, and Australia's use appears relatively stable in recent years. Box 1.1 provides an overview of the main types of aquifers and their implication on groundwater flows, not all aquifers are considered renewable, but this qualification has only a relative meaning. Table 1.2 provides the basic characteristics of the eight major aquifer systems present in OECD countries.