## 1 Introduction
CBA, with the inclusion of externalities, is an emerging tool for merging the two dimensions in the decision-making process, which can ensure economic, environmental, and social sustainability [12]. Chonburi is a province in Thailand located in the Eastern Economic Corridor (EEC), initiated by the Thai government to promote industrial growth. Water scarcity in the EEC is predicted to affect all sectors in the next 20 years [30]. Thus, there is an urgent need to place water reuse in the EEC on the policy agenda. To increase internal water reuse in industrial parks, the Industrial Estate Authority, Thailand, issued regulations requiring the reuse of at least 15% of the water supply in industrial parks established after 2015. Based on our 2018 survey, Chonburi has a high percentage of internal water reuse in industrial parks, up to 70.5%, with most industrial parks in Chonburi mainly reclaiming water for two activities: (1) industrial water supply and (2) irrigation of plants and green areas [31]. Thus, Chonburi can serve as a model for internal water reuse in industrial parks, and its data are readily available for economic feasibility analyses. Such analyses will provide valuable information for other industrial parks in Thailand and other developing countries with similar industrial park types and socioeconomic statuses. Therefore, the objectives of this study are (1) to evaluate the feasibility of water reclamation projects in industrial parks using CBA that incorporates both economic and environmental aspects, and (2) to examine the impact of environmental benefits on the feasibility of water reclamation projects in industrial parks under different scenarios (water reclamation activities, flow rates, and discount rates). This article is divided into four sections: introduction, methods, results and discussion, and conclusions. In the methods section, the background of Chonburi province is described, and the methodology of cost and benefit calculations and CBA are presented with an explanation of various water reclamation scenarios. The CBA of two water reclamation activities--that is, (1) for industrial water supply and (2) for irrigation of plants and green areas--are examined. We selected different flow rate scenarios in accordance with industrial parks in Chonburi, Thailand, which fall within the typical range for small-to-large industrial parks (Table S1). The discount rates used varied from 3% to 11%, covering those generally used for this type of project. The environmental benefits of water reclamation from not discharging pollutants into the environment were estimated using shadow prices for pollutants, which directly reflect the cost of damages if discharged to the environment. Net present values (NPVs), internal rates of return (IRRs), benefit-cost ratios (BCRs), and payback periods (PPs) were estimated and compared in cases with the inclusion and exclusion of environmental benefits. The results of the CBA are then presented in the results and discussion section, along with practical implications, recommendations for governmental support, and limitations and suggestions for future research. Lastly, all results and discussion are summarized in the conclusions. Although the inclusion of externalities in the economic analysis of water reclamation has long been proposed [28; 29], research in this area has been incomplete, particularly for water reclamation in industrial parks in developing countries. This study used the CBA framework with the inclusion of environmental benefits in real applications to examine the economic feasibility of water reclamation projects in industrial parks across a wide range of scenarios, utilizing data from industrial parks in Chonburi, Thailand, as a case study. Limitations and research gaps required for practical applications are also addressed. Moreover, shadow prices of pollutants were first applied to estimate the environmental benefits of water reclamation in industrial parks for not discharging them to the environment.