Ms. Vo Thi Hoi (Hoa Thinh village, Can Loc commune, Ha Tinh province) bought a water filter for use after being convinced by the advertisements of a seller and the results of a water quality test using a testing pen.
Ms. Hoi recounted: “The other day, several people came to measure the water in the village. Each villager brought a sample of water, then they used a measuring pen to test the water in the cup. Immediately, one of them concluded that the family's water source was not of good quality and they needed to buy a water filter to fix the water problem.”
To win her over, the establishment used the tactic of reducing the product price by nearly 50%, claiming it was a special promotional offer from a project: from 7.2 million VND down to 3.9 million VND. Hearing about the significant discount, Mrs. Hoi was overjoyed and immediately agreed to have a water filter installed.
“At first they said they would support me, then after a while they said they would support 50% of the cost for some project. I was overjoyed to hear that I was receiving support. That afternoon, someone proceeded to install the machine at my house,” added Mrs. Hoi.
Similarly, many residents in Tay Yen residential area, Thanh Sen ward, also bought water purifiers after a unit came to their homes to measure and conclude that the quality of their tap water was substandard. Notably, the water purifiers purchased by the households in Thanh Sen ward have the same model, specifications, and price of 3.9 million VND as the product sold by Ms. Vo Thi Hoi in Can Loc commune.
Ms. Pham Thi Luyen (Tay Yen residential area, Thanh Sen ward) said: "About a month ago, a unit came and asked households in the residential area to bring samples of their tap water and measure them with a pen. Afterwards, this unit concluded that the water in my house and some other households was not up to standard."
This company is currently implementing a central government project, so they're receiving support. Each machine is discounted from 7.2 million VND to 3.9 million VND. Since we have a young child at home and the discount, my family bought one of these water purifiers. We've been using it ever since, but I'm not sure if it's safe or not!
To investigate the quality of the water purifiers supplied to the aforementioned households and the company's water testing methods, following the address listed on the warranty card, the reporter visited the facility at 21 Song Cay Street, Thach Ha Commune, belonging to DES Service and Communication Co., Ltd.
Here, someone claiming to be a company employee explained to Mrs. Hoi's family and many other customers how they tested the water quality by using a TDS meter to check if the water source was safe, and then advised them on suitable water filter products.
This person stated: "To check water quality, the media uses a TDS meter. TDS is a quick test that shows the amount of heavy metals in the water. Our TDS meter has not been quality-certified."
To better understand the accuracy of the water testing pens used by this company and other establishments, the reporter purchased a bottle of Aquatta brand filtered water and took it to a well-known water filter store in Dao Market, Dong Tien Commune, for testing. As expected, the seller used a TDS meter to measure the water the reporter brought. Within minutes, the seller quickly concluded that the water in the bottle did not meet quality standards.
To further verify the quality of this bottled water, the reporter visited the supplier's location at 21 Phan Boi Chau Street, Thanh Sen Ward. There, the facility presented numerous relevant legal documents, including: a valid food safety and hygiene certificate issued by the Food Safety and Hygiene Sub-Department of the Ha Tinh Department of Health ; and water quality test results issued by the Center for Technical Standards and Quality Measurement 1, under the National Standards and Quality Measurement Committee, dated April 1, 2025.
Mr. Nguyen Anh Quy, owner of Aquata bottled water facility in Thanh Sen ward, said: “To test water quality, we have to send samples to a national testing center to check 26 indicators, not just a quick test. At the same time, the Food Safety and Hygiene Department conducts periodic inspections and takes samples every six months.”
Using a TDS meter is currently a very common method used by water filter businesses to determine the water quality for customers.
To verify the effectiveness of water quality testing using a TDS pen, a reporter searched for the keyword "TDS pen" on an e-commerce platform, resulting in thousands of products. Each TDS pen costs just over 20,000 VND, making them affordable and accessible to everyone.
TDS is a term describing the total dissolved solids in a unit volume of water, expressed in mg/L (milligrams per liter). Determining whether water is safe requires considering several factors such as pH, residual chlorine, residual arsenic, etc.
According to experts, the TDS parameter in water quality testing is also an initial basis for determining whether water quality is guaranteed. In the list of permissible limit parameters issued by the Ministry of Health in Circular No. 52 dated December 31, 2024, the limit for TDS is 1000 mg/L. This means that a TDS result below 1000 is considered acceptable. When a TDS meter shows a reading below this permissible level (usually only a few tens to a few hundred), water filter businesses immediately conclude that the water quality is not up to standard. However, this conclusion lacks sufficient basis.
Mr. Nguyen Chi Thanh, Director of the Ha Tinh Center for Disease Control, affirmed that: “To conclude whether a water sample is safe or not, many factors must be considered. Relying solely on the TDS reading from a meter is insufficient; there are also factors like bacteria, and even sensory perceptions of taste and smell. To know for sure whether the water is safe, it needs to be evaluated and tested by reputable testing centers.”
Therefore, it can be affirmed that using only a TDS meter is insufficient to conclude about water quality as advertised by businesses. Because to check water quality, rigorous and thorough testing by a competent authority is necessary.
Clearly, there has been a "glorification" of the TDS meter, which many businesses are using to verify water quality for customers, leading them to believe the water source is substandard and then spend considerable sums of money buying water purifiers. With this kind of business tactic, who can guarantee the quality of the water purifiers sold to customers?
Source: https://baohatinh.vn/chiec-but-than-thanh-va-su-that-phia-sau-man-chao-ban-may-loc-nuoc-post295290.html
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