When turning on the faucet of any home in Mexico City, the water that comes out is considered potable; that is, suitable for human use and consumption. However, the quality of the liquid can vary in the municipalities and even neighborhoods, so specialists call for caution if the decision is made to drink tap water. In cities such as Los Angeles, United States, it is common to drink a glass of water straight from the tap; in Mexico City, inhabitants usually drink and even cook with bottled water.
Mexico competes with Thailand for the position as the largest consumer of bottled water among 150 countries, with 274 liters consumed per capita per year in 2020, according to Statista. According to a 2011 Inter-American Development Bank (IDB) survey, 81% of Mexicans consume bottled water. In the capital, the Mexico City Water System (Sacmex) monitors water to ensure that it is safe to drink, so in theory, you could drink it straight from the tap.
What is the quality of water in the city?
Water quality varies depending on where you live in the city. In Iztapalapa, the most populated district with 1.8 million inhabitants, the presence of heavy metals was found in 50 wells analyzed by researchers from UAM Iztapalapa.
It is precisely the presence of these metals that when they come out of the wells and come into contact with the air when they reach homes, they oxidize, giving the water a yellow or brown color and an unpleasant odor, explains Judith Cardoso, an academic from the Physics Department of the Iztapalapa Unit.
Studies indicate that the water has this bad smell and bad color because it has an excess of two metals with these characteristics and it is due to the type of soil where it is extracted, which is rich in iron and manganese.
Diseases that can be caused by drinking tap water
Heavy metals, likely to be contained in water, can have health consequences. They accumulate in different parts of our organism such as the liver and can cause a series of problems, from gastric problems to cancer and even death. That is why it is important to be aware that these metals are not found in the water we are consuming.
Is it possible to drink tap water? At least in this district, it is not recommended. In the Iztapalapa district, which is where it is being studied, it is not feasible to drink it because it has an excess of these metals, beyond what is established by the standard NOM-127-SSA1-1994.
Warning signs in wells
A UNAM study warns of the presence of other heavy metals in 107 wells in different parts of the city, so there is a greater vulnerability to water quality located in the delegations Iztapalapa, Tláhuac, Xochimilco, Coyoacán, and to a lesser degree Milpa Alta and Azcapotzalco.
A significant increasing trend was observed for arsenic concentration in 56 wells, boron in 23 wells, iron in four wells, manganese in 60 wells, and lead in 80 wells. Current status of the aquifers, the exploitation of wells, the actual supply, and the current and potential demand for the liquid in Mexico City.
Evidence of arsenic, boron, and lead was found in the wells analyzed in cluster 3, which supply the south in municipalities such as Xochimilco, Tlalpan, and Milpa Alta. To the east of the capital, in cluster 1 corresponding to Iztapalapa and Tláhuac, high concentrations of ammonia nitrogen, chlorides, and high pH values were detected.
Ammonia nitrogen is an indicator of contamination caused by human and animal waste; in this case, it reflects possible cross-contamination between drainage pipes and the clean water distribution network.
Monitoring of the Mexico City
In the Water Quality Report, 53 samples were analyzed from household intakes in eight mayoralties, of which those located in Benito Juárez, Cuauhtémoc, Gustavo A. Madero, and Iztapalapa were within the limits in total hardness, chlorides, Iron, and Manganese.
The concentration in Coyoacán, Iztacalco, Tlalpan, and Milpa Alta is unknown as it simply indicates 'not performed', in the evaluations carried out by Sacmex from January 1, 2021, to April 8, 2022.
Regarding the concentration of chlorine, out of 111 samples of household intakes in eight municipalities of the city, 80% were within the norm during 2021. An excess was detected in only six, 89 were within the expected range, five were below, and in 11 no residual chlorine was found, based on the standards established in NOM-127-SSA-2000.