Most of the water supply plants in Hanoi which exploit underground water use outdated filtration technology which cannot eliminate toxic substances. 

Dr. Cao The Ha from the Hanoi University of Natural Sciences said the treated water samples had not been found containing concentrations of arsenic, manganese and chloride higher than Vietnam and WHO (World Health Organization) standards.

Ha said very few of the operating water plants in Hanoi use technologies that permit the standard arsenic residue at below 0.01 mg per liter.

Many plants provide water with a high arsenic concentration, including Phap Van, Luong Yen, Thanh Tri, Van Phuc and plants in the former Ha Tay province.

To eliminate solids, such as manganese, calcium, magnesium and barium, the plant uses old techniques, including spraying systems and chlorination.

The methods, according to Ha, aim to eliminate iron which helps get rid of arsenic. However, they can work only in areas with a mild arsenic content at a 1/7 ratio (one arsenic, seven iron).

A survey conducted in 2006 by water experts in eight provinces in the Red River Delta found that though underground water went through sand filtering tanks, the water taken from 20 percent of surveyed water wells in Hanoi contained arsenic.

Hung, a resident in Ha Dong district, said the technologies had been used for a century.

“Water plants said that they provide ‘clean water’. However, we often find dregs in tap water with our naked eye, and the bleach odor is very strong,” he said.

The Ministry of Health, which analyzed water samples taken from 16 water plants and seven water supply stations, found that the water did not meet five criteria.

The water samples from 20 water supply centers had a chloride residue higher than the permitted level – 0.3-0.5 mg per liter.

According to the Ministry of Health, if the chloride residue is below 0.3 mg per liter, water users may get diarrhea and other digestive diseases.

Meanwhile, if the residue is higher than 0.5 mg per liter, toxic organochlorine substances will be created, harming people’s health.

Hoang Van Thang, head of the planning division of a water supply company in Ha Dong district, admitted that the company’s filtration technology had been used for many years.

In early April, the pipeline that brings water from the Da River to Hanoi reportedly broke for the fifth time since it was put into operation in 2012. As a result, Hanoians in some areas had to use muddy water for several days until the problems were fixed.

Many Hanoians said they do not believe the “clean” water provided by the Hanoi Water Supply Company is clean enough.