Regulatory guide
NOM-127-SSA1-2021: Permissible Limits for Drinking Water
Mexico’s standard for water for human use and consumption, in force since April 2023
The full table of limits published in the DOF, what changed from NOM-127-SSA1-1994 and how a hotel, condominium or plant with its own water system complies.
- NOM:
- Mexico’s official standards
- COFEPRIS:
- Mexico’s federal health regulator
- EMA:
- Mexico’s laboratory accreditation body
NOM-127 requirements in one minute
| Parameter | Limit | Frequency |
|---|---|---|
| E. coli or thermotolerant coliforms | Not detectable in 100 mL | Monthly |
| Free chlorine residual | 0.2 – 1.5 mg/L | Daily, in a log |
| Turbidity | ≤ 3.0 NTU | Quarterly (physicochemical) |
| Total hardness (as CaCO₃) | ≤ 500 mg/L | Quarterly (physicochemical) |
Limits of NOM-127-SSA1-2021. The frequencies are our recommendation for hotels and condominiums: the standard does not set them. See the full parameter table ↓
What is NOM-127-SSA1-2021?
NOM-127-SSA1-2021 is the Mexican Official Standard that sets the permissible limits for the quality of water for human use and consumption, as well as the treatments to make it potable. It is enforced by the Ministry of Health through COFEPRIS.
Main objective
To protect public health by setting the sanitary requirements water must meet to be considered fit for human consumption: free of pathogenic microorganisms and toxic substances, and with acceptable organoleptic characteristics.Official text of NOM-127-SSA1-2021
Full text published in the Diario Oficial de la Federación (DOF) on May 2, 2022, in force since April 2023.
Who does it apply to?
It is mandatory for the bodies responsible for public and private water supply systems. In practice, anyone who operates their own well, cistern or treatment plant must comply:
- Public water supply systems (municipal utilities)
- Hotels, restaurants and other lodging facilities
- Hospitals and health centers
- Schools and educational institutions
- Industries that supply water to workers
- Condominiums and residential developments
- Any establishment that supplies drinking water
Do you manage a hotel?
Drinking water is one of six water areas at your hotel
Pools, ice, hot water, mechanical room and wastewater discharges: we cover them in one monthly program, with the compliance file ready for COFEPRIS, the Distintivo H and brand audits.
Table of permissible limits of NOM-127-SSA1-2021
Values from the text published in the DOF; in mg/L unless another unit is given
Physical specifications
| Parameter | Unit | Permissible limit | Note |
|---|---|---|---|
| Turbidity | NTU | 3.0 | 4.0 NTU in the first year; 3.0 since April 2025 |
| pH | pH units | 6.5 – 8.5 | Permissible range |
| True color | CU | 15 | Previously 20 Pt-Co units |
Chemical specifications
| Parameter | Limit (mg/L) | Note |
|---|---|---|
| Total cyanides | 0.07 | — |
| Total hardness (as CaCO₃) | 500 | — |
| Fluorides (as F⁻) | 1.50 | Phased down to 1.0 (see below) |
| Ammonia nitrogen (N-NH₃) | 0.50 | — |
| Nitrate nitrogen (N-NO₃⁻) | 11.00 | — |
| Nitrite nitrogen (N-NO₂⁻) | 0.90 | — |
| Total dissolved solids | 1000 | — |
| Sulfates (SO₄²⁻) | 400 | — |
| Methylene blue active substances | 0.50 | Detergents |
Metals and metalloids
| Metal | Limit (mg/L) | Note |
|---|---|---|
| Aluminum | 0.20 | — |
| Arsenic | 0.025 | Phased down to 0.010 |
| Barium | 1.3 | — |
| Cadmium | 0.005 | Phased down to 0.003 |
| Copper | 2.00 | — |
| Total chromium | 0.05 | — |
| Iron | 0.30 | — |
| Manganese | 0.15 | — |
| Mercury | 0.006 | — |
| Nickel | 0.07 | New in 2021 |
| Lead | 0.01 | — |
| Selenium | 0.04 | New in 2021 |
Microbiological specifications
| Parameter | Permissible limit | When it applies |
|---|---|---|
| E. coli or thermotolerant coliforms | < 1.1 MPN/100 mL or not detectable · < 1 CFU/100 mL · absent in 100 mL | Depending on the method: MPN, membrane filtration or presence-absence |
| Giardia lamblia | Absent in 20 L | Only if the source is surface water or influenced by it |
Disinfection residuals
| Parameter | Permissible limit |
|---|---|
| Free chlorine residual | 0.2 – 1.5 mg/L |
| Free iodine residual | 0.2 – 1.5 mg/L |
| Total silver | 0.05 – 0.1 mg/L |
Radioactivity, phytotoxins and byproducts
| Parameter | Permissible limit | Note |
|---|---|---|
| Microcystin-LR (phytotoxin) | 1.0 µg/L | Only with a surface water source |
| Gross alpha radioactivity | 0.5 Bq/L | — |
| Gross beta radioactivity | 1.0 Bq/L | — |
| Bromates | 10 µg/L | Disinfection byproduct |
| Chlorates and chlorites | 700 µg/L each | Disinfection byproduct |
| Formaldehyde | 900 µg/L | Disinfection byproduct |
The standard also sets limits per compound for trihalomethanes, haloacetic acids and synthetic organic compounds (benzene, toluene, xylenes and others), in its tables 10, 11 and 14.
Fluorides, arsenic and cadmium: limits phased down
Fluorides go to 1.0 mg/L, arsenic to0.010 mg/L and cadmium to0.003 mg/L, with a phase-in period that depends on the size of the locality:
| Locality | Phase-in period after entry into force | New limit applies from |
|---|---|---|
| More than 500,000 inhabitants | 1 year | April 2024 |
| 50,000 to 499,999 inhabitants | 3 years | April 2026 |
| Fewer than 50,000 inhabitants | 6 years | April 2029 |
What changed from NOM-127-SSA1-1994
NOM-127-SSA1-2021 supersedes the 2000 amendment to the 1994 standard
| Parameter | NOM-127-SSA1-1994 (2000 amendment) | NOM-127-SSA1-2021 |
|---|---|---|
| Bacteriological indicator | Total coliforms and E. coli | E. coli or thermotolerant coliforms only; Giardia if the source is surface water |
| Color | 20 Pt-Co units | 15 CU (true color) |
| Turbidity | 5 NTU | 4.0 NTU, and 3.0 since April 2025 |
| Odor and taste | “Agreeable” | No longer specified |
| Arsenic | 0.025 mg/L (since 2005) | Phased down to 0.010 mg/L |
| Fluorides | 1.50 mg/L | Phased down to 1.0 mg/L |
| Cadmium | 0.005 mg/L | Phased down to 0.003 mg/L |
| Mercury | 0.001 mg/L | 0.006 mg/L |
| Barium | 0.70 mg/L | 1.3 mg/L |
| Nitrates (as N) | 10.00 mg/L | 11.00 mg/L |
| Nitrites (as N) | 1.00 mg/L | 0.90 mg/L |
| Chlorides, zinc and sodium | 250, 5.00 and 200 mg/L | No longer listed |
| New | — | Nickel, selenium, microcystin-LR, bromates, chlorates, chlorites, formaldehyde and haloacetic acids |
What it means for a hotel in Quintana Roo
If your testing was done against the 1994 table, check above all E. coli (reporting total coliforms is no longer enough), turbidity and color. In Cancún, a locality of more than 500,000 inhabitants, the 0.010 mg/L arsenic and 1.0 mg/L fluoride limits have applied since April 2024.How often to test the water
NOM-127 sets the limits; control of distributed water is governed by NOM-179-SSA1-2020
The standard does not say how often to sample. For a hotel or condominium with its own system, this is what we recommend so you have evidence when the COFEPRIS inspection comes:
| What is measured | Recommended frequency | Who measures it |
|---|---|---|
| Free chlorine residual and pH | Daily, in a log | DPD kit or analyzer, by your own staff |
| E. coli or thermotolerant coliforms | Monthly | EMA-accredited laboratory |
| Physicochemical (turbidity, hardness, TDS, nitrates, common metals) | Quarterly | EMA-accredited laboratory |
| Toxic metals and special parameters | When the source changes or a result is out of compliance | EMA-accredited laboratory |
Our services for NOM-127 compliance
Grupo Eytra helps you comply and keep the evidence ready for inspection
Laboratory testing
In EMA-accredited laboratories, with results in 5–7 days and a report for COFEPRIS.
Water treatment
Drinking water treatment systems, automatic chlorination, filtration and UV disinfection.
Monitoring program
Sampling scheduled around your operation, with a history of results for comparison.
Documentation
Reports for COFEPRIS inspections, maintenance logs and evidence of compliance.
Practical guide
How to apply NOM-127 in your operation
What it means for hotels in the Riviera Maya
Hotels in the region face specific challenges in meeting NOM-127:
Well water quality
Most hotels in Quintana Roo draw water from deep wells in the karst aquifer. This water typically has:
- High hardness: our own tests of untreated water in the Cancún Hotel Zone range from 360 to 492 mg/L as CaCO₃ (8 analyses), which calls for softening or reverse osmosis.
- High total dissolved solids (TDS), depending on well depth and distance from the sea.
- Elevated sulfates and chlorides in coastal areas, from saltwater intrusion.
Treatment required
To comply, a typical hotel water treatment train includes:
- Prefiltration with multimedia or activated carbon
- Softening with ion-exchange resins or antiscalant dosing
- Reverse osmosis to reduce TDS and dissolved salts
- Disinfection with chlorine, UV or both
- Storage in cisterns with a controlled chlorine residual
For drinking water systems, see our water softeners and filtration and chemical treatment pages.
What it means for industry
Industrial plants that use drinking water in their processes (food, pharmaceutical, bottling) must make sure the water meets NOM-127 at the point of use. That means:
- Continuous monitoring at critical process points
- Documented records of control parameters
- Preventive maintenance of treatment systems
- Staff training in sampling protocols
For industrial plants, non-compliance can mean not only regulatory sanctions but also rejected product, recalls and damage to the brand’s reputation.
Documentation and records
COFEPRIS checks not only water quality but also document traceability. The records every water supply system must keep include:
- Laboratory test results
- Operating logs of treatment equipment
- Chemical dosing records
- Calibration certificates of measuring instruments
- Preventive maintenance programs
- Standard operating procedures (SOPs)
For daily control
NOM-127-SSA1: frequently asked questions
Common questions about drinking water quality in Mexico
What does NOM-127-SSA1-2021 establish?
The permissible limits for the quality of water for human use and consumption: physical (turbidity, pH, color), chemical, metals, microbiological, radioactive, residual and disinfection byproducts. It replaces NOM-127-SSA1-1994 and its 2000 amendment.
When did NOM-127-SSA1-2021 take effect?
It was published in the Diario Oficial de la Federación (DOF), Mexico’s official gazette, on May 2, 2022, and took effect 360 days later, in April 2023. Some limits are phased in: turbidity drops to 3.0 NTU from the second year, and fluorides, arsenic and cadmium drop over 1, 3 or 6 years depending on the size of the locality.
Who must comply with this standard?
It is mandatory for the bodies responsible for public and private water supply systems. A hotel, condominium, hospital or plant that supplies water for drinking or human use from its own well, cistern or treatment plant operates a private system and must comply.
How much chlorine should drinking water have under NOM-127?
Free chlorine residual must be between 0.2 and 1.5 mg/L. Below 0.2, disinfection is not assured; above 1.5, the water is out of compliance and the chlorine taste is noticeable.
What changed from NOM-127-SSA1-1994?
The bacteriological indicator becomes E. coli or thermotolerant coliforms; color (from 20 to 15) and turbidity (from 5 to 3.0 NTU) go down, and arsenic (to 0.010 mg/L), fluorides (to 1.0 mg/L) and cadmium (to 0.003 mg/L) are phased down. Nickel, selenium, Giardia, microcystin-LR and disinfection byproducts are added, and chlorides, zinc and sodium are removed.
What happens if my hotel’s water does not comply?
The health authority can apply the safety measures and sanctions of Mexico’s General Health Law, such as suspension of service or fines. And if a guest falls ill, the legal and reputational risk falls on the hotel. That is why it pays to have recent laboratory results and an up-to-date chlorine log.
How often should I test my property’s water?
NOM-127 sets the limits, not the frequency; control of distributed water is governed by NOM-179-SSA1-2020. For hotels and condominiums, we recommend measuring chlorine and pH daily, E. coli monthly and a physicochemical panel every quarter.
Does Grupo Eytra carry out NOM-127 testing?
Yes. We collect the samples and coordinate the tests NOM-127 requires through EMA-accredited laboratories: microbiological (E. coli), physicochemical and metals. The report supports your COFEPRIS inspection.
Does your hotel comply with NOM-127?
Testing in EMA-accredited laboratories and a compliance program for hotels and resorts in Cancún and the Riviera Maya