On December 17 2017 the National Waters Commission (CONAGUA) submitted to the Federal Regulatory Betterment Commission its draft revision of Official Standard NOM-001-SEMARNAT-1996, which establishes the maximum permissible levels of pollutants in wastewaters discharged into national waters or properties.

The draft aims to modernise the official standard by including additional terms and definitions, pollutants and parameters regarding wastewater discharge into federal waters, as well as new sampling and reporting frequency obligations.

New parameters

Under the National Waters Law and its associated regulations, any person or company required to discharge wastewater into a national water body or property can do so only by securing a wastewater discharge permit from the CONAGUA. Discharge permit holders are usually required to:

  • comply with the maximum allowable pollutant thresholds set out under the official standard;
  • take water samples during a specific period through authorised and accredited laboratories;
  • record wastewater volumes; and
  • pay wastewater duties on a quarterly basis.

The proposed amendments to the official standard introduce the following additional parameters, which could affect a wide range of industrial, commercial and agricultural operations:

  • chemical oxygen demand;
  • total organic carbon (as a substitute for chemical oxygen demand in the case of highly chlorinated discharges);
  • hydrogen potential;
  • helminth eggs;
  • escherichia coli;
  • enterococcus faecalis;
  • water colour; and
  • acute toxicity.

Conversely, the proposed amendments remove the following parameters:

  • floating material;
  • sedimentable solids; and
  • biochemical oxygen demand.

The replacement of some parameters and the inclusion of new ones are based on the need for more trustworthy and precise analysis results that can clearly evidence whether a wastewater discharge could harm an aquatic ecosystem. For instance, the inclusion of total organic carbon aims to replace the chemical oxygen demand as a parameter for highly chlorinated discharges (those showing levels above 1,000 milligrams per litre of chloride).

Sampling frequency

The draft revised NOM-001-SEMARNAT-1996 takes a more conservative approach to the frequency of sampling and reporting obligations required for municipal and non-municipal wastewater discharges:

  • For municipal discharges, the population range of 20,001 to 50,000 inhabitants has been replaced by a range of 10,001 to 50,000, which will require quarterly sampling and reporting as opposed to the quarterly sampling and bi-annual reporting required at present.
  • For non-municipal discharges, the 2,501 to 20,000 inhabitants range has been replaced with a 2,501 to 10,000 inhabitants range, which requires bi-annual sampling and quarterly reporting as opposed to the bi-annual sampling and annual reporting required at present.

Further, to determine the sampling and reporting frequency for non-municipal discharges, organic carbon and chemical oxygen demand will be considered, along with total suspended solids. This will replace the existing system, which considers only biochemical oxygen demand and total suspended solids, and eliminate the possibility of having annual reporting obligations (responsible parties will be mandated to take samples on a quarterly or bi-annual basis, as applicable). This change to the sampling and reporting frequency scheme aims to monitor risky and highly chlorinated discharges more closely.

Notwithstanding the above, NOM-001-SEMARNAT-1996 permit holders must continue to comply with other sampling and reporting obligations, such as those provided under the Federal Duties Law, which contains complementary rules for the determination of payment schemes applicable to wastewater discharges into federal bodies based on the quality of the discharge.


Although the CONAGUA's proposed changes to NOM-001-SEMARNAT-1996 may seem technical in nature, the legal implications should not be dismissed. Companies should pay close attention to the official publication of the official standard in the Federal Official Gazette, as it could change their entire compliance programme and require certified wastewater analysis laboratories to renew or update their certifications to include the new parameters. This should be of particular concern for companies which fall under the scope of the official standard, as they are required to carry out all wastewater sampling and analysis via an authorised and certified laboratory to avoid the CONAGUA deeming the results invalid.

As with all Mexican official standard update procedures undergoing public consultation via the Federal Regulatory Betterment Commission, the draft revised NOM-001-SEMARNAT-1996 is still subject to modification before its official publication and enforcement.

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