A chain is no stronger than its weakest link. The same is true at the end of water purification processes, because that is the weakest part: where human beings get involved.
Although the liquid has passed through filters and pollutant removal systems, small water purification businesses sometimes make mistakes in the bottling process, which translates into impurities in the final product, according to Andrés Vázquez Vences, water analysis manager at the ABM Laboratory in San Mateo Atenco, State of Mexico.
The specialist, a chemical engineer who graduated from the Toluca Institute of Technology, says in an interview with Tec Review that such failures, especially those related to purification staff hygiene, usually occur in the sterilization of the filling area and in the washing of the bottles, causing impurities in the water from microorganisms.
“If the water reaches a jug that is contaminated, then the water is no longer pure. After a lot of use, water jugs also get scratched and, no matter how much they are washed, bacteria will accumulate in those crevices,” explains Vázquez Vences.
That’s why Official Mexican Standard 201 on water and ice for human consumption states that the filling area must be completely isolated from other areas, and container reception and exit points must be kept closed or protected so that product contamination can be avoided during the process.
“In the case of returnable containers, they must be subjected to internal washing and disinfection, external washing, and rinsing processes. After these operations, there should be no residues of any substances used,” the document also stipulates.
However, in Vázquez’s experience, this regulation is not always fully complied with in small water bottling plants, where water jugs with a degree of microbiological contamination are sometimes sold.
Regarding the possible presence of SARS-CoV-2 in drinking water, the chemical engineer said that there is nothing to be alarmed about, as the virus causing the current pandemic has not been detected in water jugs.
The purification process step by step
There are more than 10 phases in the water purification process, ranging from adding disinfecting substances to focusing ultraviolet (UV) rays on the liquid, and including the filtering of visible and invisible particles.
Andrés Vázquez states that bottlers have tanks where the water is chlorinated, to eliminate microorganisms. Afterwards, the liquid passes into a solids tank, known as a deep bed. Its function is to remove suspended particles larger than 3 microns, which can be detected floating in the liquid by the human eye.
“Next comes the activated carbon phase, which works to remove the chlorine. Chlorine is initially added to kill bacteria, but then it has to be removed to make the water safe for drinking. At this point, the smell and taste of the water is improved. Subsequently, there is a filter known as a softener, which removes the hardness, i.e. it removes calcium carbonate from the water, and works using the ion exchange principle,” says this expert.
It is not necessary to use a softener in Mexico City and the Metropolitan Area because, in this part of the country, the hardness of the water is not so great. There is also a reverse osmosis phase that eliminates dissolved solids in the water which cannot be seen by the human eye; this is also not necessary for bottlers in the center of the country. However, in some regions of the north of the country, where there is water that is very high in solids, it is necessary to use these methods.
“Designing a purification plant for Mexico City is not the same as designing one for Hermosillo, Sonora, where heavy metals such as arsenic have been found in the water,” Vázquez clarifies.
What follows is the polisher, a phase of the process which captures any particles that may have passed the previous filters. Then, a UV lamp kills the microorganisms in the water. However, organic matter still remains there, and microscopic life can regenerate due to sunlight or the passage of time. “For this reason, the water finally passes through ozone, which acts as a preservative by oxidizing the microorganisms and thus prevents them from regenerating,” shares Vázquez.
Up to this point, according to the chemical engineer, small bottling plants usually pass all water quality examinations, but they sometimes pour it without following suitable hygiene measures into water jugs that are contaminated. This is the weakest link in the chain.