More than half of the country's key natural waterways and reservoirs show fairly good to good water quality, according to the Pollution Control Department.
PCD chief Jatuporn Buruspat on Saturday released the findings of a survey of the environmental situation last year, which he said generally represents a cause for hope due to improved public awareness of environmental protection and preservation.
The authorities have practised tougher law enforcement and implemented the government's environment policies, he said.
Mr Jatuporn said water quality was improving while deteriorated water was dropping as no new sources had been detected in the past 10 years.
He said water rated as good quality is found in sources such as the Kwai Noi River in Kanchanaburi, Songkram River in Udon Thani and the upper Tapi River in Nakhon Si Thammarat.
Deteriorated water is detected in various parts of the lower Lamtakong River in Nakhon Ratchasima, the Tachin River in Nakhon Pathom and the Chao Phraya River, among others.
The department surveyed 59 rivers and six natural reservoirs nationwide and found that 43% of them have fair water quality, 34% turned up good water quality and 23% contained deteriorated water.
Mr Jatuporn said a similar situation was found with seawater along the shorelines. Seawater quality had improved in many areas, although some parts in the Gulf of Thailand remain a hotspot for deteriorated seawater quality.
Altogether, 59% of seawater samples collected in the survey show good quality, followed by 31% as moderately good, 7% as deteriorated seawater and 2% as severely deteriorated. Only 1% was shown to be of very good quality.
Most seawater in tourist attractions falls under the category of good seawater quality such as Patong beach in Phuket and Nopparat Thara beach in Krabi.
"Waste water from households is largely responsible for polluted water," Mr Jatuporn told a press conference yesterday. He noted that swift law enforcement was needed to ensure water preservation.
Regarding air quality, provinces in the North were still encountering haze at times. The number of days haze affected the North, exceeding safety standards, was higher than in 2015 despite fewer air pollution hotspots in the long period of dry weather.
Community waste last year was around 27.04 million tonnes, or 74,073 tonnes per day, which represents an increase of 0.7% from 2015. Waste produced in Bangkok was measured at around 4.2 million tonnes per year.
Bangkok, Chon Buri, Nakhon Ratchasima, Samut Prakan and Khon Kaen are the top five waste-producing provinces.
The survey showed that 9.5 million tonnes of the yearly waste was properly managed and disposed of, 11.69 million tonnes went through improper waste management and the remaining 5.76 million tonnes was in the process of being recycled, according to the department.
Mr Jatuporn said the department's electronic waste management poses one of the pressing concerns, especially when it comes to disposing of the used mobile phones as there is no effective system to deal with them. It is estimated that there are around 200 million old mobile phones waiting for proper disposal in the country.
"We don't know where they are now. It is a challenge we must overcome by working with the mobile phone companies on how to recall the unused phones and come up with a systematic way of dealing with them.
"A campaign on the issue is going to be launched in line with the electronic waste management law, which will be enforced in the future," Mr Jatuporn added.
Last year, 686 complaints were lodged with the authorities airing environmental problems involving air, noise and waste, and 25 chemical accidents were reported.