Thailand
Last Updated : 09 April 2025.
Thailand's water environment is diverse and vital to the nation's ecological balance, economy, and people's livelihoods. The country's geography, with its extensive coastline, rivers, and wetlands, presents a rich tapestry of aquatic ecosystems. Although the exact number can vary depending on the classification criteria, there are approximately 231 major rivers and 3,220 small rivers in Thailand. In addition, there are over 2,000 natural and artificial lakes scattered across the country.
State of water environment
Thailand is divided into 22 river basins, as defined in the Royal Decree on River Basin Boundaries, B.E. 2564 (2021). These river basins can be further divided into 353 sub-basins and include six island groups within the main river basins (ONWR 2022). In 2023, Thailand experienced an average annual rainfall of 1,408 mm, which was 95 mm or approximately 6% lower than normal. Most areas of the country experienced below-normal rainfall, although patches of above-normal rainfall were also observed, particularly in the lower south, from Nakhon Si Thammarat Province to the southern tip of the country. This rainfall pattern contrasted sharply with 2022, when all regions experienced above-normal rainfall. The significant reduction in rainfall in 2023 highlights the variability and challenges in water resource management that Thailand faces due to changing climatic conditions.
Less rainfall in 2023 resulted in less water flowing into the dams. All 35 large dams across the country experienced a total annual inflow of 40,980 million cubic meters (m³), a drop of 13,074 million m³ compared to the previous year and almost equivalent to the capacity of Bhumibol Dam. However, it still represented a relatively large annual inflow compared with historical data over the past 10 years. A total of 38,193 million m³ was released, the fourth highest after 2018, 2022, and 2017. At year-end, the remaining water storage in the 35 dams was 54,621 million m³, or 77% of total dam capacity. This was a moderate water level, slightly decreased from the previous year, with usable water amounting to 31,084 million m³.
Compared with historical data over the past 10 years (2014-2023), 2023 witnessed the third highest amount of water remaining at the end of the year, following 2017 and 2022. Two dams overflowed, 15 dams had high water levels, 14 dams had moderate water levels, four dams had low water levels, and no dams had critically low water levels (National Hydroinformatics Data Center, 2023).
Please read: Outlook 2024 Thailand
Legal framework
Legislative framework for water quality management (Source: WEPA Outlook 2024):
- Enhancement and Conservation of National Environmental Quality Act (B.E. 2535) (Translated in English; Outside source: FAO)
- Groundwater Act (B.E. 2520) (Translated in English; Outside source: DGR)
- Factory Act (B.E. 2535) (Translated in English; Outside source: JETRO)
- Public Health Act (B.E. 2535) (Translated in English; Outside source: MOPH)
- Hazardous Substances Act (B.E. 2535) (Translated in English; Outside source: DIW)
- Building Control Act (B.E. 2522) (Translated in English; Outside source: AIPA LYNC)
Institutional arrangement
Institutional arrangement of water environment management (Source: WEPA Outlook 2024)
The institutional arrangement related to water management in Thailand operates under the Thai cabinet. The National Water Resources Committee (NWRC) was established, with the Office of the National Water Resources (ONWR) serving as the secretariat. There are subcommittees for each of the 22 river basins, and technical management together with implementation committees have been formed to address issues in specific areas.
As part of water quality management, the Ministry of Natural Resources and Environment (MoNRE) operates through the Pollution Control Department (PCD) and its Water Quality Management Division to propose policies addressing various issues, such as establishing effluent standards for pollution control from point sources to meet ambient environmental quality standards. These efforts are supported by regional offices, including the Environmental and Pollution Control Offices (EPO 1–16) throughout Thailand, which manage local-level problems. Additionally, other departments under MoNRE, such as the Department of Groundwater Resources (DGR), oversee both the quantity and quality of groundwater resources. The Department of Water Resources also plays a crucial role in managing flood and drought situations.
In addition to water management, various related ministries and their departments also play significant roles. These include the Department of Meteorology, the Department of Disaster Prevention, the Department of Public Works and Town and Country Planning, the Land Development Department, the Royal Irrigation Department, the Metropolitan Waterworks Authority, the Provincial Waterworks Authority, the Electricity Generating Authority of Thailand (EGAT), and other relevant organizations.
Water quality standards
Water Quality Standard (on pp.12-13)