“The magical TDS pen” and the truth behind the water purifier sales pitch in Ha Tinh

Ms. Vo Thi Hoi (Hoa Thinh village, Can Loc commune, Ha Tinh province) bought a water purifier for use, after being convinced by the advertisements of a machine seller and the results of water quality testing with a test pen.

Mrs. Hoi recounted: “The other day, some people came to measure the water in the village. Each person brought a sample of water, then they used a measuring pen to put it in a cup of water. Immediately, this person concluded that the family's water source was not of good quality and that a water filter should be purchased immediately to fix the problem with the water source."

Ms. Vo Thi Hoi (Hoa Thinh village, Can Loc commune) bought a water purifier after the seller concluded that her family's water quality was not guaranteed.

To make her feel better, the facility applied a tactic of reducing the product price by nearly 50% and asserted that this was a special preferential policy of a project: from 7.2 million VND to 3.9 million VND. Hearing the news of the deep discount, Mrs. Hoi was "happy inside" and immediately agreed to install a water filter for use.

“At first they said they would support me, then after a while they said they would support 50% according to a certain project. After hearing that, I was immediately happy to be supported. That afternoon, someone installed the machine at my house,” Ms. Hoi added.

Mrs. Hoi agreed to buy the water purifier immediately because of the nearly 50% discount.

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 concluded that the quality of domestic water was not guaranteed. Notably, the water purifiers that the households in Thanh Sen ward bought had the same model, information and the same selling price of 3.9 million VND as the product of Ms. Vo Thi Hoi in Can Loc commune.

Ms. Pham Thi Luyen (Tay Yen TDP, Thanh Sen Ward) said: "About a month ago, a unit came to call on households in the residential group to bring samples of domestic water and measure it with a pen. After that, this unit concluded that the water in my house and some other households was not safe.

This company is currently implementing a project from the Central Government so it is supported. Each machine is discounted from 7.2 million VND to 3.9 million VND. There is a small child in the house and the discount is also available, so my family bought a water purifier of this type. We have been using it since the purchase, but I don't know if it is guaranteed!"

Ms. Pham Thi Luyen (Tay Yen Residential Group, Thanh Sen Ward) bought a water purifier after hearing the seller conclude that her water was not safe.

The water purifiers of households in Tay Yen Residential Group, Thanh Sen Ward match the machine of Ms. Vo Thi Hoi (Can Loc Commune) in terms of design, shape, price, label, information, and seller's address.

To learn about the quality of the water purifiers provided to the above households and the company's water testing method, following the address listed on the warranty card, the reporter approached this facility at No. 21, Song Cay, Thach Ha Commune, belonging to DES Services and Communications Company Limited.

Here, a person claiming to be a company employee explained how to test water quality to Ms. Hoi's family and many other customers by using a TDS test pen to see if the water source was safe, and then proceeded to advise on water purifier products.

This person said: “To check the water quality, you guys should use a TDS pen. TDS is a quick test that shows the heavy metal content in the water. Our TDS pen is not quality tested.”

To better understand the accuracy of the water testing pen used by this company and other establishments, the reporter bought a bottle of purified water branded Aquatta and went to a reputable water purifier store in Dao market, Dong Tien commune to test it. As expected, the seller used a TDS pen to measure the water index that the reporter brought. Just a few minutes later, the seller quickly concluded that the water in the bottle was not of good quality.

A shop owner in Dong Tien commune measured the water brought by a reporter... and concluded that it was not of good quality.

To further verify the exact quality of this bottle of water, the reporter went to the supplier located at 21 Phan Boi Chau Street, Thanh Sen Ward. Here, the facility presented many related legal procedures such as: the facility meets food safety and hygiene conditions as licensed by the Department of Food Safety and Hygiene under the Ha Tinh Department of Health ; the water quality test results were issued by the Technical Center for Standards and Quality Measurement 1, under the National Committee for Standards and Quality Measurement on April 1, 2025.

Mr. Nguyen Anh Quy, Aquata bottled water facility, Thanh Sen ward said: "To test the water quality, we have to send samples to the national measurement center to test 26 indicators, not just a quick test like that. At the same time, the Department of Food Safety periodically checks and takes samples every 6 months."

Reporters witnessed all relevant legal documents and test results from the National Quality Standards Committee for Aquata bottled drinking water.

Using TDS pen is currently a very popular form that water purifier businesses use to conclude the quality of water sources for customers.

To verify the quality of water testing with a TDS pen, the reporter searched for the keyword “TDS pen” on an e-commerce platform, the results showed thousands of products. Each TDS pen costs only from over 20 thousand VND, anyone can buy and measure.

TDS pens are sold widely on e-commerce platforms.

TDS is a term that describes the total dissolved solids in a unit volume of water, expressed in mg/L (milligrams per liter). To determine whether water is safe or not, it is necessary to rely on many indicators such as pH, residual chlorine content, residual arsenic...

According to the professional agency, the TDS parameter in water quality testing is also an initial basis for determining whether the water quality is guaranteed or not. In the list of allowable parameters issued by the Ministry of Health in Circular No. 52 dated December 31, 2024, the TDS limit is 1000 mg/L. That means a TDS result below 1000 is an allowable index. And when the TDS test pen shows a parameter below this allowable level (usually only a few dozen to a few hundred), water purifier businesses immediately conclude that the water does not ensure water quality. But this conclusion is not fully grounded.

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, we must rely on many factors. If we only rely on the TDS index on the measuring pen to conclude, it is not enough, there are also groups of bacteria, including from sensory taste. And if we want to know exactly whether the water is safe or not, it needs to be evaluated and tested by reputable testing centers.”

Mr. Nguyen Chi Thanh, Director of Ha Tinh Center for Disease Control, affirmed that the TDS index on the measuring pen is not enough basis to conclude water quality.

Thus, it can be affirmed that using only TDS pen tool is not enough to conclude about water quality as advertised by businesses. Because to check the quality, there needs to be strict testing, full process from competent authorities.

Obviously, there has been a "deification" of the TDS pen that many businesses are using to verify the water quality for customers, to convince them that the water source is not of guaranteed quality, and then spend a lot of money to buy water purifiers. And with this kind of business trick, who dares to affirm the quality of the water purifiers that have been sold to customers.

Source: https://baohatinh.vn/chiec-but-tds-than-thanh-va-su-that-phia-sau-man-chao-ban-may-loc-nuoc-o-ha-tinh-post295290.html