The main part of a transboundary aquifer analysis is usually the assessment of its hydrogeological situation. Herewith, the main steps of a methodology for assessment of internationally shared aquifers are described. In principle, application of the hydrogeological methods is the same for national and international aquifers. More internationally specific are the processes of classification and zoning of the aquifers. Data comparison and harmonisation across the border is the main technical challenge. Non-technical challenges are primarily related to other aspects of TBAs, such as socio-economical and political situation in the border region.

The assessment of the shared groundwater could be seen as composed of the following steps:

• Delineation and description
• Classification, diagnostic analysis and zoning
• Data harmonisation and information management

The first two activities (delineation and description) could be clustered as ‘inventory' or ‘characterisation', depending on the stage and the scale of activities. In any case, delineation and description are chiefly about collecting, combining and interpreting the field information.

Hydrogeological Scope

The second set of activities provides the stakeholders with information necessary for decision-making, such as on problems that may develop and opportunities that will be forgone in the absence of coordinated groundwater resources development and management. Further on, the stakeholders need to know which aquifers are likely to be most the responsive ones to transboundary aquifer management, and which zones within such aquifers should be targeted for highest positive impacts.
 
One could argue whether the activities mentioned in the third step should be addressed separately; data harmonisation takes place in the previous steps and the information management is a management measure. Nevertheless, data harmonisation and information management have an additional dimension and importance in the international content; they are more difficult to carry out, more elaborated and politically sensitive. At the same time, they are also an opportunity for building trust and mutual understanding among the involved parties.