What Mexico's discharge rules cost an industrial plant

A Mexican plant that discharges to a river, an arroyo, a canal or a drain sits inside a tax rule as well as an environmental one. Article 282 of the Ley Federal de Derechos exempts a discharger from the federal discharge duty in any quarter when its effluent stays within the permissible limits. The exemption also requires that the site meter the volume at every discharge point and hold an analysis from a laboratory accredited and approved by CONAGUA for that quarter. Miss one parameter in one quarter and the exemption falls away, and the rate in Article 277-B applies to the cubic meters discharged.

At the amounts in force for 2024, that rate runs from 21.46 to 47.32 pesos per cubic meter for a private discharger paying under fracción II, depending on whether the receiving body is classed A, B or C. A plant that has accredited its activity with CONAGUA under fracción III pays 6.91 to 15.29 pesos per cubic meter for a biodegradable discharge, and 17.56 to 38.78 pesos for a non-biodegradable one. Same water, same outfall, three times the price.

The exposure therefore turns on two documents rather than on a treatment plant: the quarterly laboratory report measured against NOM-001-SEMARNAT-2021, and the filing that moves the site off the default rate. Our earlier note on industrial water challenges in Mexico covers the operating side. This piece covers the instruments and the money.

What the permit and the standard require

The Ley de Aguas Nacionales was enacted by the Congress of the Union and published in the Diario Oficial de la Federación on 1 December 1992. CONAGUA administers it. It issues the discharge permit, receives the reporting and collects the duty. It does not write the statute, and it does not set the discharge limits.

Article 88 requires a CONAGUA permit to discharge into national waters. Article 88 BIS, last reformed in the DOF on 8 May 2023, sets out what the permit holder then owes. The site must keep measuring devices and sampling access points in working order. Volume and quality reports must rest on determinations by laboratories accredited under the federal metrology law and approved by the water authority. Monitoring records must be kept for at least five years, and any process change that alters the volume or character of the effluent has to be notified.

The limits come from NOM-001-SEMARNAT-2021, published in the DOF on 11 March 2022, which replaced NOM-001-SEMARNAT-1996. Its parameter tables took effect on 3 April 2023. True color and acute toxicity apply later, from 11 March 2026.

The 2021 standard changed what is measured, not only how much is allowed. Five-day biochemical oxygen demand, floating matter and settleable solids came out of Table 1. Chemical oxygen demand came in. Nitrogen and phosphorus limits now apply across every class of receiving body.

For discharges to rivers, arroyos, canals and drains, the monthly average limits are 150 mg/L for chemical oxygen demand and 60 mg/L for total suspended solids. Fats and oils are capped at 15 mg/L, total nitrogen at 25 mg/L and total phosphorus at 15 mg/L. pH has to sit between 6 and 9 and temperature at or below 35 degrees Celsius. Send the same effluent to a reservoir, lake or lagoon and chemical oxygen demand tightens to 100 mg/L and total phosphorus to 5 mg/L. Send it to soil for irrigation of green areas and chemical oxygen demand tightens to 60 mg/L.

Table 2 adds the metals. To a river the monthly averages include 0.2 mg/L for arsenic, cadmium and lead and 0.01 mg/L for mercury. To a reservoir those fall to 0.1 mg/L and 0.005 mg/L.

Where the money sits

Article 278-A of the Ley Federal de Derechos classifies each receiving body as type A, B or C, and the rate follows that class. Two plants with identical effluent can pay different amounts on the same volume. The 2024 amounts are below.

Pesos per cubic meter, amounts in force for 2024.

Fracción III is not automatic. The Reglas de Carácter General published in the DOF on 27 February 2014 set out what a taxpayer has to present to prove the activity that produces the discharge. A plant that never filed under those rules pays the fracción II rate by default.

Take an illustrative discharge of 100,000 cubic meters a year into a type C body. On that illustrative volume the gap between the fracción II rate and the biodegradable fracción III rate would be about 3.2 million pesos a year. That is arithmetic on the published rates, not a result measured at any plant.

The duty is assessed and paid quarterly, so exemption and exposure both reset four times a year. A clean quarter buys no protection for the next one.

Sewer or national water body

The question that decides which rulebook applies is where the outfall goes. Effluent sent to an urban or municipal sewer falls under NOM-002-ECOL-1996, published in the DOF on 3 June 1998, and the counterparty is the municipal or state water utility, not CONAGUA.

The two sets of limits are far enough apart to change a treatment decision. NOM-002 allows 50 mg/L of fats and oils as a monthly average, against 15 mg/L under NOM-001. It allows pH from 5.5 to 10, against 6 to 9, and 40 degrees Celsius against 35. Cadmium is capped at 0.5 mg/L to sewer and 0.2 mg/L to a river.

The same effluent can therefore clear the sewer connection and breach a river outfall. A plant that changes discharge route, or whose municipal operator restricts intake, moves between the two regimes with no change in process. On our read, the sewer route also takes the site out of the federal discharge duty and puts it under the operator's tariff and local reglamento instead.

What a cubic meter of reuse is worth

Reuse is usually argued on the water bill. The federal abstraction duty is the larger and more variable number. Article 223, apartado A of the Ley Federal de Derechos charges by availability zone, and sets the amount at 29.3655 pesos per cubic meter for groundwater in zone 1 and 2.8769 pesos in zone 4. Surface water runs from 21.7931 pesos to 2.5156 pesos across the same zones.

A cubic meter not abstracted is worth more than ten times as much in a zone 1 municipality as in a zone 4 one, before the utility charge and before any discharge duty avoided. A reuse case that clears the hurdle rate at one site can fail at another site in the same company. The zone is fixed by municipality in the law, so the first input to a reuse model is the zone, not the equipment quote. Groups building water management support into a capital plan should price each site on its own zone. The same two figures, cubic meters abstracted and cubic meters reused, are what an assurance provider asks to see for ESG and social risk work.

What a breach costs beyond the duty

Article 120 of the Ley de Aguas Nacionales, as reformed by the decree published in the DOF on 6 January 2020, sets fines in three bands running from 260 UMA to 26,000 UMA according to the infraction. INEGI announced on 9 January 2024 that the UMA would stand at 108.57 pesos a day from 1 February 2024. That puts the range at roughly 28,000 pesos to 2.8 million pesos.

The fine is rarely the binding constraint. Article 122 of the same law goes further. For most of the infractions in Article 119 it orders temporary or permanent closure, partial or total, of the works or the discharge point on top of the fine, and Article 120 adds revocation of the title and permanent closure where the plant reoffends. A partial closure order on an outfall stops the production line feeding it. That exposure, not the fine, is what a treatment retrofit should be costed against.

What to have on the desk this quarter

• Confirm the outfall regime in writing. A national water body puts the site under a CONAGUA permit and NOM-001-SEMARNAT-2021. A municipal sewer puts it under the utility and NOM-002-ECOL-1996.
• Pull the last four quarterly analyses and set them against the correct column of Tables 1 and 2 for the receiving body class. The standard sets a monthly average, a daily average and an instantaneous value, so check all three.
• Check which fracción of Article 277-B the site is charged under, and whether the fracción III accreditation was ever filed under the 2014 Reglas de Carácter General.
• Price treatment only for the parameters that fail. Chemical oxygen demand, fats and oils, nitrogen and phosphorus sit on different unit processes at different costs.
• Put 11 March 2026 in the compliance calendar for true color and acute toxicity, and take a baseline measurement well before that date.

Check your effluent against your permit limits

Mexico Energy Partners compares a site's last four quarters of effluent analyses against the limits in its discharge permit and the applicable standard, names the parameters at risk, and returns costed treatment or reuse options with the electrical consumption of each. Send the discharge permit, the last four quarterly declarations, the laboratory analyses for the same periods, and the site water balance. We confirm the receiving body class and the Article 277-B fracción being applied before anything is priced.

Sources

• Diario Oficial de la Federación, Ley de Aguas Nacionales, 1 December 1992, Articles 88, 88 BIS, 119, 120 and 122. Article 88 BIS last reformed 8 May 2023.
• Diario Oficial de la Federación, decree reforming the Ley de Aguas Nacionales, 6 January 2020, amending the fines in Article 120.
• Diario Oficial de la Federación, NOM-001-SEMARNAT-2021, 11 March 2022, Tables 1 and 2 and the transitory articles.
• Diario Oficial de la Federación, NOM-002-ECOL-1996, 3 June 1998, Table 1 and the pH and temperature provisions.
• Diario Oficial de la Federación, decree reforming the Ley Federal de Derechos, 13 November 2023, in force 1 January 2024.
• Diario Oficial de la Federación, Ley Federal de Derechos, Articles 223, 277-B, 278-A and 282, as in force in 2024 following the decree of 13 November 2023.
• Diario Oficial de la Federación, Reglas de Carácter General on Article 277-B, fracción III, 27 February 2014.
• INEGI, press release 10/24 on the value of the Unidad de Medida y Actualización, 9 January 2024.