2025 Thailand water quality assessment: PCD annual report
Decade of monitoring shows Thailand's water resources are holding steady, with Andaman coast leading in purity, and no surface water sources falling into Highly Polluted category in 2025.
- The 2025 PCD report indicates that most of Thailand's coastal and surface water is in "Fair to Good" condition, with data showing quality is either stabilizing or slightly improving over the past decade.
- Of the 210 coastal sites monitored, 91% were rated "Fair" or "Good," while 9% were classified as "Polluted" or "Highly Polluted," with high nutrient and bacteria levels being a primary concern.
- Surface water quality assessment across 363 stations showed 86% rated "Fair" or "Good," with a notable success being that no areas were classified in the worst "Highly Polluted" category.
The Pollution Control Department (PCD) has released its 2025 Thailand Water Quality Situation Report, revealing positive trends.
Most coastal and surface water resources nationwide remain in "Fair to Good" condition.
Data from the past decade suggests that water quality is either stabilising or slightly improving, reflecting progress in national monitoring and resource management, though certain areas require continued vigilance.
Surin Worakijthamrong, Director-General of the PCD, stated that in 2025, the department monitored 210 coastal sites across six types of water usage zones using the Marine Water Quality Index (MWQI).
Coastal Water Quality Highlights
The assessment shows:
- 31% rated as "Good"
- 60% rated as "Fair"
- 9% combined rated as "Polluted" or "Highly Polluted"
Top 10 Best Coastal Water Quality Areas:
- Saphli Bay, Chumphon
- Bo Muang Bay, Krabi
- Klong Dao Beach, Krabi
- Thung Wua Laen Beach, Chumphon
- Ban Klong Nin, Koh Lanta, Krabi
- Haad Rin, Koh Phangan, Surat Thani
- Thai Mueang Beach, Phang Nga
- Lamai Beach, Koh Samui, Surat Thani
- Koh Kai, Krabi
- Bang Son Bay, Chumphon
- Chao Phraya River Estuary, Samut Prakan
- Klong 12 Thanya Estuary, Samut Prakan
- Dyeing Factory Zone (KM. 35), Samut Prakan
- Bang Khun Thian, Bangkok
- Tha Chin River Estuary, Samut Sakhon
Long-term Trends: Over the last 10 years (2016–2025), coastal water quality has remained relatively stable, with the Andaman Coast consistently ranking the highest.
However, high levels of nutrients and bacteria remain a primary concern, which could trigger more frequent "Plankton Blooms" if left unmanaged.
Surface Water Quality Results
The PCD also monitored 363 stations across 59 main rivers and 6 standing water bodies between January and September 2025.
Using the Water Quality Index (WQI), the results were:
- 40% "Good"
- 46% "Fair"
- 14% "Polluted"
- 0% "Highly Polluted" (No areas fell into the worst category)
Top 10 Best Surface Water Resources:
- Upper Phetchaburi River
- Upper Tapi River
- Un River
- Nong Han Lake
- Phum Duang River
- Songkhram River
- Khwae Noi River
- Upper Lang Suan River
- Loei River
- Phong River
Monitoring over the past decade shows a slight upward trend in quality.
The absence of "Highly Polluted" surface water reflects successful collaboration between government agencies, the private sector, and local communities in water restoration and monitoring.
Surin emphasised that the PCD will continue regular monitoring to provide essential data for national policy and wastewater management.
He urged the public and private sectors to remain conscious of their environmental impact to ensure Thailand’s water resources remain sustainable for future generations.
