The serious drought situation in the Eastern Region in B.E. 2548 was caused by lacking of main water sources and high variability of rainfalls in the Region thus unable to support the expansion of industry in Rayong Province. This situation prompted the necessity to develop new water resources management tools to create the appropriated solution alternatives in the area together with the social processes to build up understanding of all stakeholders on the problems and the agreeable and implementable solution alternatives. Therefore, the research project “the Development of the Area-based Water Resources Information System with the Decision Support System and Social Process in Rayong Province: Phase I” was initiated, developed and implemented the System with the participation of the local administrative organizations (LAO). The LAO provided and keyed in inputs on water and its related resources into the System through the network thus created an updated and trustworthy database. Subsequently the LAO used the processes data from the System to prepare an up-todate water resources management plan, particularly for the estimation and assessment of local water conditions and preparation of emergency plan, and as a tool for supporting the development activities of the local districts. However, after the initial implementation of Phase I, it was found that the developed System was not yet fully capable of integrating and linking with the potential improvement activity in the coordination of the network at the river basin level. This Research Study Phase II Project expanded the development of the Water Resources Information System to improve its efficiency and effectiveness in supporting users of all levels (policy/operation/local) by implementing it with the collaborations and supports of users in the local districts. These improvements were divided in 3 elements: 1) The improvement of the System’s data/information. By regularly up-dating it to maintain the continuity of various databases, previously developed during Phase I, all of which were taken from the Provincial Operation Center (POC) and since POC had reduced its role in maintaining the databases. In this Study Phase data/information has been updated together with certain software of the Systems. Furthermore the System was improved to fit and support various needs of users on water data/information in the local districts such as: the operation of water trucks; the village water supply system; the reserved water sources; and the agro-information of the local districts in order to directly facilitate the resolving of the problems of the local districts together with the development of the data verification system. 2) The improvement of engineering techniques. In Phase I various tools were developed to assist the analyses and decisions on the assessment of water balance in Rayong Province. Such tools included: data input-output; data calculation and estimation; as well as data display systems. The estimations covered: rainfalls; runoffs and inflows into reservoirs. The analyses covered: quantity of reserved water sources; shallow and deep groundwater usages; domestic, agricultural and industrial water usages. After actual implementation of the System in the local districts certain improvements in the calculation and engineering techniques were added, including advanced forecasting and assessment of future water situation and water usages, alternatives in water allocation that were more appropriate and accessible by users. 3) The improvement of the data and knowledgebase system. Through the study on various social organizations which had roles or participated in the decisionmaking processes to develop the water users database and through the study of the past and present proposed solution alternatives in the district, as divided by regions, river basins and district, the knowledge base system that supported participatory mechanism was improved. This was achieved through the preparation of various user manuals such as: the User Manual for the Water Resources Information, the Water Supply System, the Program Q-GIS, etc. to impart knowledge to users and theirs associates. This knowledge base covered and responded to the needs of the local districts. It comprised curriculum on the guidelines for resolving water resources problems for the practitioners/operators in 3 subjects, i.e. (1) the preparation of the district water account; (2) the construction cost estimation for a small weir, the estimation of water quantity in the water pond, and the guidelines for solving water problems using village maps; (3) the preparation of water supply map of the village. In addition the methods for comparative analysis on the economics and benefits of two solution alternatives for water shortages, i.e. constructing village water supply and running water trucks were prepared and disseminated.