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In 1996, Con was hired by his school to test water samples from a suburb in Hanoi. More than 10 out of 30 water samples were found having arsenic concentration much higher than the permitted level.

He then decided to learn more about the underground water situation in Hanoi.

Later, Con created a water map of Hanoi, showing the areas contaminated with arsenic. These included eight water plants in the inner city and self-dug water wells in the suburbs. 

Up to 30 percent of surveyed wells were found having arsenic concentration at over 0.05 mg/l, while 50 percent were over the permitted level of 0.01 mg/l.

Con realized that people only filtered underground water manually to eliminate iron, while the measures they applied could not eliminate arsenic. 

Later, Con helped people eliminate arsenic from underground water by using laterite.

Thousands kinds of materials were used by Con in his experiments to find the best way to filter water and eliminate toxic organic substances in water. 

After many years of working, Con has found materials which are cheap but useful in filtering water. 

These include clay from Truc Thon, stone from Deo Mountain and coconut shell charcoal from Tra Bac. 

Con has tried to apply nanotechnology to renew polluted water.

He finally created a water filtration technology, which “cannot be found in any other country in the world”.

At first, Con used the technology to filter tap water and water from Bay Mau Lake in Hanoi.  

The filtered water was then brought to the Institute of Hygiene and Epidemiology Center and General Directorate of Measurement and Quality Control for testing. 

As the tests gave very satisfactory results, Con then tried to filter the water from To Lich River, which is considered the most polluted water in Hanoi and called Hanoi’s “black water village”.

The water from To Lich, black and smelly, after going through Con’s water filtration units, turned clean and pure enough for drinking. 

The purity of the water filtered by Con has been officially recognized by important agencies in Vietnam.

Experts have repeatedly warned about the dangers of exploiting underground water in Hanoi, saying that the water is seriously polluted, especially in the low land areas.

Ten years ago, inspection agencies discovered higher than permitted nitrogen concentration in water of the Phap Van water supply station, also in Hoang Mai District. Phap Van also took running water from exploited underground water.