Environmental regulations
NOM-002-SEMARNAT-1996: Discharges to Sewer Systems
Still in force: there is no NOM-002-SEMARNAT-2021. Maximum permissible limits for wastewater discharges to urban or municipal sewers, with the official PDF.
- NOM:
- Mexico’s official standards
- SEMARNAT:
- Mexico’s environment ministry
- EMA:
- Mexico’s laboratory accreditation body
- Tested in EMA-accredited laboratories
- Results in 15–25 days
NOM-002 requirements in one minute
| Parameter | Limit | Frequency |
|---|---|---|
| pH | 5.5 – 10 | Quarterly (minimum) |
| Fats, oils and grease | ≤ 50 mg/L (monthly average) | Quarterly (minimum) |
| Settleable solids | ≤ 5 mL/L (monthly average) | Quarterly (minimum) |
| Temperature | ≤ 40 °C | In every sample |
The utility sets the frequency; with high discharge volumes it can be monthly or every two weeks. See the full parameter table ↓
What is NOM-002-SEMARNAT-1996?
NOM-002-SEMARNAT-1996 is the Mexican Official Standard that sets themaximum permissible limits for pollutants in wastewater discharges to urban or municipal sewer systems. Its purpose is to protect the sewer infrastructure and the operation of municipal treatment plants.
Important
Unlike NOM-001-SEMARNAT-2021, which governs discharges to national water bodies, NOM-002 applies specifically to discharges to the municipal sewer. Local utilities can set stricter limits depending on the conditions of their system.Official text of NOM-002-SEMARNAT-1996
Download the full text from the PROFEPA website (Mexico’s environmental enforcement agency). Official reference document in force.
Scope of the standard
It is mandatory for every individual or company that discharges wastewater to urban or municipal sewer systems. The limits apply to domestic, industrial, commercial and service discharges alike.
Do you manage a hotel?
Your sewer discharge is one of six water areas at your hotel
Pools, ice, hot water, mechanical room and drinking water: we cover them in one monthly program, with the compliance file ready for COFEPRIS, the Distintivo H and brand audits.
Parameters and maximum permissible limits
Maximum values allowed for discharges to the municipal sewer system
| Parameter | Unit | Monthly average | Daily average | Instantaneous |
|---|---|---|---|---|
| Fats, oils and grease | mg/L | 50 | 75 | 100 |
| Settleable solids | mL/L | 5 | 7.5 | 10 |
| Total arsenic | mg/L | 0.5 | 0.75 | 1 |
| Total cadmium | mg/L | 0.5 | 0.75 | 1 |
| Total cyanide | mg/L | 1 | 1.5 | 2 |
| Total copper | mg/L | 10 | 15 | 20 |
| Hexavalent chromium | mg/L | 0.5 | 0.75 | 1 |
| Total mercury | mg/L | 0.01 | 0.015 | 0.02 |
| Total nickel | mg/L | 4 | 6 | 8 |
| Total lead | mg/L | 1 | 1.5 | 2 |
| Total zinc | mg/L | 6 | 9 | 12 |
In addition: pH from 5.5 to 10 and a temperature of 40 °C at most in every grab sample, and no floating matter. For BOD₅ and total suspended solids, the standard refers to table 2 of NOM-001-ECOL-1996 or to the specific conditions of the municipal discharge (section 4.6); if they are not met, joint treatment at the municipal plant can be agreed, with the discharger paying its cost (section 4.7).
Who must comply?
Sectors and establishments required to comply with NOM-002-SEMARNAT
Hotels and resorts
Lodging establishments that discharge wastewater to the municipal system.
Industrial plants
Factories, maquiladoras (export assembly plants) and manufacturing operations that discharge to the sewer.
Restaurants and kitchens
Food and beverage establishments with high levels of fats, oils and grease.
Hospitals and clinics
Healthcare facilities whose wastewater can contain special pollutants.
Car washes
Vehicle washing businesses that discharge detergents and oils.
Condominiums and residential developments
Residential developments with a shared discharge to the municipal sewer.
Consequences of non-compliance
Legal and operating risks of not complying with NOM-002-SEMARNAT
Fines
Municipal authorities can impose significant fines for exceeding the permissible limits for pollutants in discharges.
Sewer disconnection
The municipal sewer utility (organismo operador) can suspend the connection, preventing the establishment from operating.
Legal liability
Damage to the sewer system or the municipal treatment plant can lead to civil and criminal liability.
Closure
In serious cases, the authorities can order the temporary or permanent closure of the establishment.
How Grupo Eytra helps
Sampling, testing and treatment so your discharge meets NOM-002-SEMARNAT
Assessment
Full analysis of your current discharges to identify parameters out of compliance.
Solution
Design of pretreatment systems: grease traps, settling tanks, pH neutralization.
Implementation
Equipment installation, start-up and training of your operating staff.
Monitoring
Periodic testing and compliance reports for the municipal utility.
Practical guide
How to comply with NOM-002, step by step
Prohibited substances
NOM-002 strictly prohibits discharging the following substances to the sewer:
- Flammable liquids with a flash point below 93 °C
- Hazardous waste as defined by NOM-052-SEMARNAT
- Radioactive substances
- Sludge from wastewater treatment systems
- Waste or residues that can block the sewer
Specific discharge conditions (CPD)
An important aspect of NOM-002 is that municipal water utilities can set specific discharge conditions (condiciones particulares de descarga, CPD) stricter than the standard’s limits. This happens when:
- The municipal treatment plant has limited capacity
- The sewer system has structural problems
- Industrial discharges affect the treatment process
- The sanitation infrastructure needs protecting
In Cancún and the Riviera Maya, CAPA (the state water and sewer commission) and AGUAKAN can set CPD that include additional parameters such as BOD₅, COD or total nitrogen.
Monitoring frequency
How often to sample and test depends on the specific discharge conditions set by the utility, but as a general rule we recommend:
| Discharge volume | Recommended minimum frequency |
|---|---|
| Less than 3,000 m³/month | Every six months |
| 3,000 to 30,000 m³/month | Quarterly |
| More than 30,000 m³/month | Monthly |
Samples must be tested by an EMA-accredited laboratory (Entidad Mexicana de Acreditación, Mexico’s accreditation body), and the results delivered to the utility within the required deadlines.
Types of sample
- Grab (instantaneous) sample: taken at a specific moment. Used for pH, temperature and floating matter.
- Composite sample: made up of at least 4 grab samples taken at equal intervals during the discharge period (at least 4 hours). Used for fats, oils and grease, settleable solids and heavy metals.
Verification and compliance
Who verifies compliance?
Unlike NOM-001 (where CONAGUA is the authority), under NOM-002 the municipal water utility verifies compliance and imposes penalties. In Quintana Roo, the main bodies are:
- CAPA (Comisión de Agua Potable y Alcantarillado, the state water and sewer commission)
- AGUAKAN (the concession holder in the north of the state, including Cancún)
- Municipal utilities in other localities
Obligations of the discharger
- Obtain the discharge permit from the utility
- Sample at the frequency set in the CPD
- Deliver test results to the utility
- Keep a record of discharge volumes
- Report process changes that alter the quality of the discharge
- Install pretreatment if pollutants exceed the limits
How to comply with NOM-002
Step 1: Characterize your discharge
The first step is to know the quality of your current discharge through a full laboratory analysis. This tells you whether you meet the limits or need a pretreatment system.
Step 2: Assess whether you need pretreatment
If your discharges exceed the limits, you will need a pretreatment system. The most common include:
- Grease traps: for restaurants, hotels and food establishments
- Neutralization systems: for discharges with pH out of range
- Settling tanks: to remove settleable solids
- Coagulation-flocculation systems: for industrial discharges with heavy metals
Step 3: Set up a monitoring program
Set a sampling schedule according to the utility’s CPD. Hire an accredited laboratory and keep an organized file of all results.
Step 4: Keep records
Document discharge volumes, test results, maintenance on the pretreatment system and any incidents. These records are your best defense in an inspection.
NOM-002-SEMARNAT: frequently asked questions
Common questions about discharges to sewer systems
Is there a NOM-002-SEMARNAT-2021?
No. The standard in force for wastewater discharges to urban or municipal sewers is NOM-002-SEMARNAT-1996. The one that was updated is NOM-001-SEMARNAT-2021, which governs discharges to receiving bodies that are federal property and does not apply to discharges to the municipal sewer.
What is the difference between NOM-001 and NOM-002?
NOM-001-SEMARNAT governs wastewater discharges to national receiving bodies (rivers, lakes, the sea, soil), while NOM-002-SEMARNAT applies to discharges to the urban or municipal sewer system. The permissible limits differ because water discharged to the sewer is treated afterwards at the municipal treatment plant.
Which parameters are exceeded most often?
The parameters most commonly exceeded are fats, oils and grease (especially in restaurants and hotels), BOD₅ and total suspended solids. In industry, heavy metals such as chromium and lead are also frequent problems. A proper pretreatment program can solve these exceedances.
How often should I test my wastewater?
The monitoring frequency depends on the specific discharge conditions set by the municipal utility. As a minimum, we recommend quarterly testing. For dischargers with high volumes or a history of non-compliance, the frequency can be monthly or even every two weeks.
What happens if I do not comply with NOM-002?
Non-compliance can lead to fines from the municipal utility, extra charges for additional treatment, disconnection from the sewer service and, in serious cases, temporary or permanent closure of your facilities. You may also face civil liability for damage to the sewer system.
Can Grupo Eytra arrange the required testing?
Yes. We collect the samples and coordinate, through EMA-accredited laboratories, all the tests needed to verify compliance with NOM-002-SEMARNAT: physicochemical parameters (pH, temperature, fats, oils and grease, TSS, BOD₅, settleable solids) and heavy metals. The report comes from an EMA-accredited laboratory, and we advise you on corrective measures if you are out of compliance.
Do your hotel’s discharges comply with NOM-002?
Discharge testing and pretreatment systems for hotels and resorts in Cancún and the Riviera Maya