In the second episode of the IWA YWP Thailand “Next Wave” podcast, Dr. Chawalit Chaiwong sat down with host Dr. Thitiwut Maliwan (Chulalongkorn University) to unpack Thailand’s wastewater situation, from Bangkok’s canal network to the case for treating used water as a resource instead of discarding it.
Thailand has the laws, the technology, and the research base to manage its wastewater. According to Dr. Chawalit Chaiwong, a senior research associate at the Global Water & Sanitation Center (GWSC) at the Asian Institute of Technology (AIT), what’s still missing is far more basic: getting the wastewater to a treatment plant in the first place.
The gap isn’t technology. It’s collection.
Dr. Chawalit has spent the past four to five years on wastewater treatment and reuse, after more than a decade in sanitation research. He breaks Thailand’s wastewater down into three sources: industry, agriculture, and households. Industrial wastewater, he says, is already managed reasonably well. Community wastewater is where the country’s real problem sits.
It isn’t a shortage of policy or know-how. Thailand already has the regulations, the treatment technology, and the research base. What’s missing, in his view, is coverage: the infrastructure to actually collect wastewater from households and buildings before it reaches a treatment plant. Add rapid urban growth on top of a budgeting pattern that still treats wastewater as a cost rather than a resource, and the gap between policy and practice keeps widening.
Bangkok shows the pattern at scale. The city has eight large-scale centralized treatment plants, covering roughly 60–70% of its area, and even inside that coverage zone, not all the wastewater reaches a plant. Some of it goes straight into the canals untreated. Bangkok’s canals run more than 2,000 kilometers, but according to Dr. Chawalit, they have no real natural source, except the Chao Phraya River: More than 40% of canal water comes from treated wastewater discharge, and the rest arrives from other rivers and canals. Where treatment coverage falls short, it shows up directly in canal water quality.
From “wastewater” to “resource”
The idea Dr. Chawalit has spent recent years developing, water reuse, starts from a different premise than conventional treatment. Instead of treating water to a discharge standard and releasing it, water reuse treats it to whatever quality a specific job requires, then puts it back into use.
“Once wastewater has been treated and its quality improved, it isn’t ‘bad’ anymore. If we can turn that dirty water back into good water, at a quality appropriate for certain activities, we might not even need to call it ‘wastewater’ anymore.”
— Dr. Chawalit Chaiwong, AIT
He points to two examples from the project work. At Future Park Rangsit, wastewater from handwashing and general building use goes through the treatment units plus UV (ultraviolet) disinfection, then gets reused for toilet flushing: a non-contact use that avoids the higher cost of treating water to a standard fit for direct human contact. At the Bangkok Metropolitan Administration, only about 10% of the treated wastewater from the city’s eight plants gets reused, mainly for watering plants and washing floors. The limit isn’t demand. It’s regulation, and how intensively the water has been treated.
Nature doesn’t need electricity
Dr. Chawalit’s more recent research pairs water reuse with Nature-based Solutions: constructed wetlands, green roofs, and green walls that lean on plants, soil, and natural microbial processes instead of UV, ozone, or membrane filtration. None of this is new science. Constructed wetland technologies have been used to treat wastewater for 10 to 20 years. What’s changed is why people are looking at them again.
“We don’t need to treat water back to 100% of its original state — we just need it to serve whatever purpose it’s going to be used for, in a way that’s worth the cost of treatment.”
— Dr. Chawalit Chaiwong, AIT
Dr. Chawalit’s data shows nature-based systems running on roughly 20–40% less energy than conventional options like UV, ozone, and membrane filtration. That’s a real difference for utilities watching long term operating budgets, even if treatment efficiency runs a bit lower.
There’s a perception angle too. Communities near treatment plants often assume they’re unclean, so Bangkok started calling its facilities “water quality control plants” instead of “wastewater treatment plants.” Nature-based systems reinforce that shift just by looking like gardens instead of machinery. They’re also flexible enough to work in dense urban sites and rural communities alike.
What this means
Dr. Chawalit holds a PhD in Environmental Engineering and Management from AIT, focused on water and wastewater engineering. His work covers treatment technology, sanitation, and resource recovery and reuse, carried out at GWSC under the leadership of Prof. Thammarat Koottatep, the center’s co-director. Prof. Thammarat’s focus on practical, deployable sanitation solutions has shaped much of GWSC’s work with partners such as UNICEF, SEA-Map, Gates Foundation and more.
The pattern Dr. Chawalit describes, solid law, solid technology, weak coverage and low prioritization, isn’t unique to wastewater. But it’s a useful diagnostic for where policy attention would do the most good. Closing the collection gap, clarifying water quality standards for reuse, and funding nature-based pilots at scale would move Thailand’s wastewater management forward more than any single new treatment technology.
Key Facts:
- Bangkok has 8 large-scale centralized wastewater treatment plants, covering roughly 60–70% of the city.
- About 70-80% of water used in daily activities in Bangkok becomes wastewater.
- Roughly more than 40% of the water in Bangkok’s 2,000+ km canal network comes from treated wastewater discharge.
- Only about 10% of treated wastewater from the Bangkok’s 8 large-scale treatment plants is currently reused.
- Nature-based treatment systems use roughly 20–40% less energy than conventional UV, ozone, or membrane filtration systems.
Topics: WASH · Water Reuse · Circular Economy · Nature-based Solutions · Wastewater Management · Bangkok
About GWSC: The Global Water & Sanitation Center (GWSC) at the Asian Institute of Technology provides research, capacity development, and technical advisory to advance WASH outcomes. gwsc.ait.ac.th | gwsc@ait.ac.th