Parameters for physicochemical analysis of water for standard 127 NOM-127-SSA1-2021 in Mexico

What physicochemical analyses of water are performed to meet the 127 standard for drinking water?

The parameters of physicochemical analysis of water set by NOM-127-SSA1-1994 and the new NOM-127-SSA1-2021 for human use, which comes into force this year 2023, require a certain number of water tests to check the permissible limits of water quality and the treatments it receives for its potabilization.

Updates between Nom 1994 and 2021

Update of permissible limits:

• • The 2021 standard updates several permissible limits to improve public health protection based on the latest international research and recommendations.

Inclusion of new compounds:

• • New compounds to be controlled have been added in the 2021 standard that were not specified in the 1994 version, reflecting a greater understanding of the potential health risks.
  • New Organic Compounds and their Limits in NOM-127-SSA1-2021
    1. Fixed adsorbable halogenated organic compounds:
       • Hexachlorobutadiene: 0.60 µg/L
       • Pentachlorophenol: 9.0 µg/L
       • 2,4,6-Trichlorophenol: 200 µg/L
       • Epichlorohydrin: 0.40 µg/L
    2. Halogenated pesticides:
       • Atrazine: 100 µg/L
       • Terbuthylazine: 7.0 µg/L
    3. Halogenated herbicides:
       • 2,4-D: 30 µg/L
       • 2,4,5-T: 9.0 µg/L
       • 2,4-DB: 90 µg/L
    4. Non-halogenated organic compounds:
       • Carbamates and other semi-volatile compounds such as Aldicarb: 10 µg/L
       • Polyaromatic Hydrocarbons as Benzo(a)pyrene: 0.70 µg/L
    5. Phosphorous pesticides:
       • Chlorpyrifos: 30 µg/L
       • Dimethoate: 6.0 µg/L

Test methods and treatments:

• • The test methods for determining water quality and the required drinking water treatments have been updated and specified in more detail in the 2021 standard.

Gradual compliance:

• • The 2021 standard introduces a phased-in compliance system for certain parameters, allowing smaller localities to adjust to the new standards over an extended period.

The Official Mexican Standard NOM-127-SSA1-1994 and NOM-127-SSA1-2021 establish the sanitary requirements that the quality of water for human use and consumption in Mexico must meet. Below is a comparison of the parameters of both standards:

Cyanides

NOM-127-SSA1-1994 establishes the maximum permissible limits for contaminants in treated wastewater discharged into receiving water bodies in Mexico, including the maximum permissible limit for cyanide.

The maximum permissible limit of cyanide in treated wastewater discharged into receiving water bodies, according to the standard:

NOM-127-SSA1-1994, is 0.2 mg/L (milligrams per liter).

NOM-127-SSA1-2021, is 0.7 mg/L (milligrams per liter).

It is important to note that cyanide is a highly toxic substance and its presence in concentrations above permissible limits can pose a risk to human health and the environment. Therefore, it is necessary to ensure that wastewater is adequately treated before discharge into receiving water bodies and to comply with the permissible limits established by the standard.

Free residual chlorine

Chlorides

The maximum permissible limit of chloride in treated wastewater discharged into receiving water bodies, according to the standard

NOM-127-SSA1-1994, is 250 (as Cl-) mg/L (milligrams per liter).

Chloride is a naturally occurring substance in water and can be released into the environment through human activities, such as wastewater discharge. If chloride levels in water are too high, they can affect water quality and aquatic life. Wastewater treatment facilities must have adequate processes in place to ensure that their effluent is sufficiently treated before discharge into receiving water bodies and must comply with the permissible limits set by the standard.

Color scale Pt-Co

The Pt-Co color scale is a measure of the color intensity of a water sample, which is determined by visual comparison of the sample with a Pt-Co color scale. The presence of high concentrations of organic matter, heavy metals and other contaminants can contribute to increased water color.

NOM-127-SSA1-1994 regulates the maximum permissible levels of color and turbidity for treated wastewater discharged into receiving water bodies. The maximum permissible color limit on the Pt-Co scale is 150 units (U.C.), while the permissible turbidity level is 0 to 0.15 NTU.

High concentrations of organic matter, heavy metals and other pollutants can contribute to increased water color, which can negatively affect aquatic life.

Total hardness

Water hardness refers to the amount of calcium and magnesium minerals dissolved in water, and can affect its quality and its use for different purposes. It is measured in milligrams per liter (mg/L) of CaCO3 (calcium carbonate). NOM-127-SSA1-1994 establishes the maximum permissible limit for total hardness at 500 mg/L in treated wastewater discharged into receiving water bodies.

High hardness levels can cause scaling and corrosion problems, as well as difficulties in foaming during cleaning processes. It is important to monitor and control hardness levels to protect water quality and the environment.

Phenols

NOM-127-SSA1-1994 limits the concentration of phenols in treated wastewater discharged into receiving water bodies to 0.5 mg/L or less. The NOM establishes that the maximum allowable limit for phenols in treated wastewater discharged into receiving water bodies is 0.5 mg/L (milligrams per liter).

Industrial wastewater may contain substances such as phenols, which can interfere with aquatic life and affect water quality. It is important to monitor the levels of phenols in wastewater and to comply with the permissible limits established by the standard.

Fluorides

An important aspect of treating wastewater containing fluorides is to maintain low levels through the use of appropriate processes, chemicals and equipment. The standard establishes maximum allowable limits for the discharge of treated wastewater containing fluorides into receiving water bodies to protect water quality and minimize anthropogenic impacts on aquatic ecosystems.

Mexico’s National Standard (NOM-127-SSA1-1994) establishes that the maximum allowable limit for fluorides in treated wastewater discharged into receiving water bodies is 15 mg/L (milligrams per liter). Exceeding this limit can be toxic to human health and aquatic life. In order to protect the environment, it is important to control fluoride levels in wastewater and comply with the permissible limits established by the standard.

Ammonia nitrogen

Ammonia nitrogen is a chemical compound that can be toxic and harmful to aquatic life in high concentrations, and is released into the environment through human activities, such as the discharge of wastewater from some industries and agricultural activities. Therefore, it is important to control the levels of ammonia nitrogen in wastewater and comply with the permissible limits established by the standard to protect water quality and the environment.

The maximum allowable limit for ammonia nitrogen in treated wastewater discharged into receiving water bodies, according to NOM-127-SSA1-1994, varies depending on the type of receiving water body:

• For water bodies intended for drinking water supply, the maximum allowable limit is 0.5 mg/L (milligrams per liter) of N-NH3 (ammonia nitrogen).
• For water bodies that are not intended for drinking water supply, the maximum allowable limit is 2.0 mg/L N-NH3.

Nitrate nitrogen

In nature, nitrates are necessary to produce proteins and support the growth of plants and animals. However, when present in high concentrations, they can be harmful to humans and aquatic life.

According to NOM-127-SSA1-1994, the maximum allowable limits for nitrate nitrogen (NO3) in treated wastewater discharged into receiving water bodies vary according to the type of receiving water body.

• For water bodies intended for drinking water supply, the maximum allowable limit is 10 mg/L (milligrams per liter) of N-NO3 (nitrate nitrogen).
• For water bodies that are not intended for drinking water supply, the maximum allowable limit is 20 mg/L of N-NO3.

Nitrite nitrogen

Nitrites are chemical compounds that form in water from the oxidation of nitrates, and can be harmful to human health if consumed in high concentrations.

Nitrites can interfere with the blood’s ability to carry oxygen, which can cause cyanosis (bluish discoloration of the skin and mucous membranes), headaches, dizziness and other symptoms. In addition, nitrites can react with other compounds to form nitrosamines, which are carcinogenic compounds.

NOM-127-SSA1-1994 establishes a maximum permissible limit of 1 mg/L (milligrams per liter) for nitrite nitrogen content in water intended for human use and consumption. This limit applies both to drinking water supplied by public water supply systems and to bottled water for human consumption. It is important to note that this limit is designed to ensure the safety of water for human consumption and to protect public health.

Odor in water

Odor is a sensory parameter that can be used as an indicator of water quality, and it is important to control it to prevent the emission of bad odors that can affect public health and the environment. The maximum allowable odor limit established by the standard is based on the Odor Unit (OU) methodology, which is a standard measurement to quantify the odor level of a substance or water sample.

The maximum allowable odor limit for treated wastewater discharged into receiving water bodies is 5 odor units per cubic meter (5 u/m³) in accordance with NOM-127-SSA1-1994 .

PH

A pH parameter serves to indicate the degree of acidity or alkalinity of a solution. The pH value is an important factor that can affect water quality. The standard establishes the permitted pH range, ensuring that treated wastewater discharged into receiving water bodies is neither too acidic nor too alkaline, which can adversely affect water quality and the environment.

NOM-127-SSA1-1994, Tratamiento de Acueductos y Alcantarillados, specifies that the maximum permissible pH limit for treated wastewater discharged into receiving water bodies is 6 to 9 pH units.

Flavor in water

The standard establishes maximum allowable limits for other organoleptic parameters of treated wastewater, such as the maximum allowable limit for color, odor and turbidity. These parameters are important to ensure that treated wastewater is aesthetically acceptable and does not present odor or appearance problems, which can affect water quality and public health.

Total dissolved solids

Total dissolved solids (TDS) refers to the total amount of dissolved materials in water, including salts and minerals. The maximum allowable TDS level is established to ensure that treated wastewater discharged to receiving water bodies does not contain an excessive concentration of dissolved solids that could affect water quality.

According to NOM-127-SSA1-1994, the maximum permissible limit for TDS in treated wastewater discharged to receiving water bodies is 1,500 milligrams per liter (mg/L).

Sulfates

NOM-127-SSA1-1994 establishes the permissible limits for various chemical and microbiological parameters in water, including sulfates. According to the standard, the permissible limit for sulfates in water intended for human consumption is 250 mg/L (milligrams per liter).

It is important to note that this limit only applies to water intended for human consumption and not necessarily for other uses, such as agricultural irrigation or industry.

Methylene blue active substances

NOM-127-SSA1-1994 establishes a maximum permissible limit of 0.1 mg/L (milligrams per liter) of methylene blue in water for human use and consumption. This limit applies to all forms of water intended for human consumption, including drinking water, bottled water, and packaged water. Methylene blue is a dye that is used in a variety of applications, including tissue staining in histology and as an indicator in chemical tests. However, its consumption in large quantities can be toxic to human health.

Turbidity in water

Turbidity is a measure of water clarity and is related to the amount of suspended particles in the water. Water with high turbidity may contain particles that affect the taste, odor, color and microbiological quality of the water, so the standard establishes this limit to ensure the quality of water intended for human consumption. High turbidity of water may be due to natural processes or contamination.

NOM-127-SSA1-1994 establishes a maximum permissible limit of 5 nephelometric turbidity units (NTU) for water intended for human consumption.

The turbidity limit established in the standard applies to water intended for human consumption and not necessarily to other uses, such as industry or agricultural irrigation.

Heavy metal analysis of water to comply with standard 127

Likewise, NOM-127-SSA1-1994 establishes a series of analysis parameters for metals to measure water quality:

Aluminum

NOM-127-SSA1-1994 establishes the permissible limits for contaminants in water for human use and consumption in Mexico. In relation to aluminum, this standard establishes a maximum permissible limit of 0.2 mg/L (milligrams per liter) in drinking water. It is important to note that this limit may vary in different countries and in different regulations, so it is necessary to check the specific regulations of each place to know the corresponding permissible limits.

Arsenic

According to NOM-127-SSA1-1994, n relation to arsenic, this standard establishes a maximum permissible limit of 0.025 mg/L (milligrams per liter) in drinking water for contaminants in water for human use and consumption in Mexico. This limit may vary in different countries and in different regulations.

Barium

Barium is a heavy metal that can be toxic to human health if found in high levels in water. It is used in a variety of industries, such as oil, mining and ceramics manufacturing, among others.

The maximum permissible limit of 0.7 milligrams of barium per liter of water was established in the standard based on the criteria and recommendations of international organizations such as the World Health Organization (WHO), which consider this level of barium in water to be safe for long-term human consumption.

It is important to note that the standard establishes other maximum permissible limits for various contaminants in water, and that compliance with these limits is the responsibility of drinking water supply systems and public health authorities.

Cadmium

Cadmium is a heavy metal that can be toxic to human health if ingested at high levels. Cadmium is found in a variety of consumer products, including food, water and tobacco, among others. Chronic exposure to cadmium can cause harmful health effects such as kidney damage, osteoporosis, lung damage and cancer.

Copper

Copper is an essential element for human health in adequate amounts, but can be toxic in high concentrations, especially to the liver and nervous system. Copper may be present in water due to corrosion of copper pipes, as well as mining, smelting and other industrial processes.

Chrome

Chromium is a metal used in various industries, such as metallurgy and chemicals, and may be present in water as a result of waste discharge processes. Exposure to elevated levels of chromium in water can be toxic to human health, causing adverse effects such as skin irritation, respiratory problems and liver damage.

The maximum permissible limit for total chromium in water for human consumption, according to Mexican Official Standard NOM-127-SSA1-1994, is 0.05 milligrams per liter (50 micrograms per liter).

Iron

Iron is a mineral that helps the body produce red blood cells and maintain normal levels of hemoglobin, or oxygen-carrying cells in the blood. It is also necessary for the proper functioning of nerves and energy production by muscles. In addition to being present in many foods and nutritional supplements, however, it can produce an unpleasant metallic taste when consumed in high levels in water, cause health problems such as diarrhea and gastrointestinal disorders.

Because of this, NOM-127-SSA1-1994 establishes that the maximum permissible limit of iron in water is 0.3 milligrams per liter.

Manganese

Manganese is a mineral that occurs naturally in soil and water and is important for human health in small amounts. However, if it is consumed in high levels in water, it can produce a bitter taste and affect the appearance and quality of the water.

The maximum permissible limit for manganese in water for human consumption, according to Mexican Official Standard NOM-127-SSA1-1994, is 0.5 milligrams per liter, in order to ensure that the water is safe for use.

Mercury

Mercury is a toxic metal that can be released into the environment as a result of human activities such as mining and burning fossil fuels. Exposure to elevated levels of mercury can cause nervous system damage, kidney disorders and other adverse effects on human health.

Due to the risk that this metal represents to human health, the maximum permissible limit for mercury in water for human consumption, according to Mexican Official Standard NOM-127-SSA1-1994, is 0.001 milligrams per liter (1 microgram per liter).

Lead

Lead is a toxic metal that is released into the environment through human activities such as industry, mining and the burning of fossil fuels. Exposure to elevated levels of lead can cause nervous system damage, kidney disorders, anemia and other adverse effects on human health, especially in children. In addition to being common in urban air, lead particles are also found in household dust and soil due to emissions from automobiles and industrial processes. When it comes to protecting yourself and your family from lead poisoning, it is critical to know how to clean it up.

Therefore, it is important to have a limit for this metal in water. According to the Mexican Official Standard NOM-127-SSA1-1994, the limit is 0.01 milligrams per liter (10 micrograms per liter).

Sodium

Sodium is a mineral that occurs naturally in water and is necessary for the proper functioning of the human body. However, excessive sodium intake can increase the risk of high blood pressure and other health problems, especially in people with pre-existing conditions. Therefore, it is important that drinking water supply systems regularly monitor sodium levels in water and take measures to reduce them if they are above the levels recommended for human consumption.

According to NOM-127-SSA1-1994, the range of sodium concentration in water for human consumption is 25 to 200 milligrams per liter. However, it is recommended that sodium concentrations not exceed 100 milligrams per liter in water for human consumption, in order to prevent arterial hypertension in susceptible persons.

Zinc

While zinc is an essential mineral for the human body in small amounts, it can become toxic in excess. Zinc can enter drinking water through soil and rock dissolution processes, as well as through release from industry and other human processes.

Therefore, NOM-127-SSA1-1994 establishes this maximum permissible limit of zinc in water for human consumption, in order to protect the health of the population. This limit is 5 milligrams per liter.

Microbiological water analysis for drinking water standard 127

NOM-127-SSA1-1994 establishes a series of analysis parameters for microbiological organisms that help keep water fit for human use.

Fecal coliform analysis

Fecal coliform analysis is used to determine the microbiological quality of drinking water. These microorganisms are commonly found in the intestinal tract of humans and other animals, and their presence in drinking water may indicate the possible presence of other pathogenic microorganisms.

Mexican Official Standard NOM-127-SSA1-1994 establishes that drinking water must be free of pathogenic microorganisms, including fecal coliforms. Therefore, the maximum permissible limit for fecal coliforms in drinking water is zero (0) in 100 milliliters.

Total coliforms

Total coliform analysis is used to determine the microbiological quality of drinking water. Total coliforms are a group of microorganisms commonly found in the environment, and their presence in drinking water may indicate the possible presence of other pathogenic microorganisms.

For this parameter, Mexican Official Standard NOM-127-SSA1-1994 establishes that the maximum permissible limit for total coliforms in drinking water is 5 in 100 milliliters.

Sceherichia coli

Eschericha coli (E. coli) is a bacterium found in the intestine of humans and other animals. Its presence in drinking water may indicate the possible presence of other pathogenic microorganisms and poses a health risk to people who consume the water.

Due to the risk to human health, Mexican Official Standard NOM-127-SSA1-1994 establishes that drinking water must be free of pathogenic microorganisms, including Escherichia coli. Therefore, the maximum permissible limit for E. coli in drinking water is zero (0) in 100 milliliters.

Trihalomethanes analysis

NOM-127-SSA1-1994 also establishes a test to measure the concentration of trihalomethanes in water.

Total trihalomethanes

Total trihalomethanes (TTHMs) are chemical compounds formed when chlorine is used to disinfect drinking water containing organic matter. Although non-toxic at low concentrations, TTHMs are considered to be carcinogenic at high concentrations and their long-term presence in drinking water may increase the risk of cancer.

To avoid any risk situation for human health, the Mexican Official Standard NOM-127-SSA1-2021 establishes that the maximum permissible limit for total trihalomethanes in drinking water is 0.1 milligrams per liter (mg/L) or parts per million (ppm).

We do not have the service to perform these analyses, we suggest you go to a laboratory certified by CONAGUA: Comisión Nacional del Agua (conagua.gob.mx) in its laboratory search engine by state.

If you need to comply with the 127 standard for water purification, come to us with an analysis of the parameters you need to comply with to help you.