Aquifers are not visible (although ecosystems associated with aquifers sometimes are, for example wadis and oases). Consequently, there may be a need to characterize the waterbody and ensure countries recognize the existence and shared nature of the system as a pre-condition to starting the TDA.
Because aquifers are difficult to visualize, It will be necessary to carefully consider how to describe the size and scale of the water system; the causes of the identified transboundary or shared problems (for example using a hot spot approach for abstraction); and the impacts, both environmental and socio-economic.
Many of the environmental problems facing aquifers will be shared rather than transboundary. For example, the TDA for the Nubian Sandstone Aquifer was renamed a Shared Aquifer Diagnostic Analysis because of this very issue.