Municipal Wastewaters in Mexico. Reflections on a Challenge

BACKGROUND
Mexico faces water insecurity of multiple dimensions that threatens the achievement of sustainable development. Although great progress has been made in recent decades, there are still structural challenges that hinder ensuring access to drinking water in sufficient quantity and good quality at a fair price, so that people can meet their basic needs for consumption, health, hygiene, and sanitation; use ecosystems sustainably so that they continue to provide their environmental services; ensuring an adequate supply of water to produce goods and services, and strengthening the population’s capacity to withstand the impacts associated with extreme hydrometeorological events intensified by climate change.

Abandoned wastewater treatment plants.

 Juan Manuel Morgan-Sagastume

Challenges of the water sector are faced with infrastructure that has generally exceeded its useful life; with financing that shows a gradual decrease in investment rates, and with a governance model that has not been able to integrate the diverse values of water when establishing and implementing fair, equitable, and sustainable water policies.

Mexico lacks management plans necessary to promote the adequate treatment of wastewater, both at the municipal level and in the industrial sector. This problem has existed for decades: six-year terms begin and end without having adequately addressed the challenge that persists in the matter.

At the end of 2024, 2899 plants are reported with an installed capacity of 194,913 liters per second and a treated flow of 143,769 liters per second, that is, a treatment coverage of 68.1 percent (SEMARNAT-CONAGUA, 2025) of the generation of municipal wastewater in the country, which is around 211,114 liters per second.

Lack of sanitation causes severe health crises, such as the spread of diarrheal diseases (cholera, dysentery), parasitic infections, and hepatitis A. It also leads to serious contamination of water sources, the destruction of ecosystems, poverty, and often high remediation costs. The perverse cycle of poverty-less water-greater poverty is exacerbated. According to a 2012 World Health Organization study (OMS, 2024), every U.S. dollar invested in sanitation yields a return of 5.5 dollars, translated into lower health care costs, higher productivity, and fewer premature deaths.

CAUSES
The problem has multiple variables and must be treated with this premise to find a solution. There are documents dating back decades that explain the causes of the problem (SMISAAC, 1987): over-designed and under-used infrastructure, last-minute public spending, projects for population growth without drainage, illegal diversion of wastewater for agricultural irrigation, inadequate selection of technology for wastewater treatment plants (WWTPs), which does not consider regional environmental and socio-economic aspects (particularly for small to medium-sized WWTP, that is, less than 200 liters per second); inappropriate design of plants that, on many occasions, prioritize poor quality equipment to lower costs; mis-location in dry riverbeds that flood during the rainy season; strikes motivated by community pressures due to negative impacts such as noise and odors, and inadequate social management and information to the community about wastewater treatment projects that makes them be perceived as harmful, which causes attitudes against their establishment.

Abandoned wastewater treatment plants.

  Juan Manuel Morgan-Sagastume

“Delicate” equipment is frequently specified—such as instruments (dissolved oxygen sensors, pH, ultrasonic meters), general electronic circuits, dosing pumps, “ozonation” and ultraviolet radiation systems, as well as systems with membranes—which are continuously damaged due to lack of maintenance and spare parts. Many WWTPs have been found to malfunction due to overloads caused by illegal industrial discharges. Lack of training, coupled with excessive substitution of operating personnel in WWTPs, results in empirical operation without analytical oversight. Vandalism and theft at facilities occur often. There are not the necessary financial resources for the operation and maintenance of WWTPs, particularly in plants that are highly mechanized and require a lot of electricity for their operation.

In addition to the above, there is little technical information in Mexico about the design and operating conditions of WWTPs, which is especially unfavorable if a study is to be carried out or engineering is to be developed for improvement or rehabilitation. 

In general, the State hardly distributes resources for the management of the country’s waterheds. There are no comprehensive strategies nor planning that consider all actors and stakeholders for the sanitation of waterheds in their true dimension, with the aim of protecting the environment and improving the quality of life. However, it is worth highlighting a current federal project, the Strategic Water Project for the Valley of Mexico, which shows firm steps to begin to partially solve this challenge. 

Article 115 of the Political Constitution of the United Mexican States, in the subsection a) of fraction III, determines that the public service of drinking water, as well as the sewerage, drainage, treatment, and disposal of wastewater, is a direct and exclusive responsibility of municipalities. The obligation to manage the infrastructure and offer these services to citizens, with the possibility of coordinating with the state or the federation, if necessary, is part of this municipal competence; however, the vast majority of the country’s municipalities lack financial and technical resources to fulfill this mandate. This scarcity is mainly due to the inability to adequately charge for the water services provided to the population, largely because of an incomplete comprehension of the human right to water.

Abandoned wastewater treatment plants.

 Juan Manuel Morgan-Sagastume

Article 115 assigns operational responsibility, while Article 4 of the Constitution (amended in 2012) establishes the human right to water. The latter requires that the supply be sufficient, healthy, acceptable, and affordable, which requires municipalities to ensure these standards, something very complicated without the appropriate financial resources, technical knowledge, planning and management; political will is required on the part of the State to face this challenge. 

The State knows the problem, we just need to read the National Water Program (PNH) 2014-2018 (CONAGUA, 2017) to know. The synthesis of this situation is clear and evident. The diagnosis of the situation has been repeated in subsequent PNH, but so far no appropriate and complete plan has been presented for the whole country to deal with the problem and solve it definitively.

NEED FOR FINANCIAL RESOURCES
According to the information published in the national inventory of municipal drinking water treatment and wastewater treatment plants in operation as of December 2024, the main causes behind non-operative plants were maintenance (34.5 percent), operation (28.6 percent), rehabilitation or expansion processes (24.1 percent), obsolescence of infrastructure (11.4 percent) and damage due to hydrometeorological problems (1.4 percent). With this data, we can assume that obsolete and damaged plants do not operate; the rest (87.2 percent) do or have the potential to operate with adjustments. 143,769 liters per second of treated wastewater are officially reported; 67,345 liters per second are pending to reach 100 percent (that is, 211,114 liters per second of municipal wastewater generated).

It should be considered that the vast majority of the existing infrastructure in the field of wastewater treatment at the moment probably continues to comply with the already repealed standard NOM-001-SEMARNAT-1996, since there has been no time or resources to convert these plants so that they can comply with the new standard NOM-001-SEMARNAT-2021, published on March 11, 2022 in the Official Gazette of the Federation. This norm, as a characteristic to be highlighted, focuses on the elimination of nutrients for discharge into water bodies. There are several challenges to be faced; how to address them is discussed in Morgan-Sagastume (2022).

It is estimated that to rehabilitate a WWTP the amount of investment is around 800 000 pesos for each treated liter per second, while a new WWTP may require—according to the author’s experience—an investment of two million pesos for every treated liter per second. Rehabilitation considers the use of existing infrastructure. If the cost of rehabilitating the existing WWTPs to meet the new standard is added to the investment cost for new infrastructure, the amount of investment needed is close to 250 billion pesos is required.

To visualize the investment required in another way, it is compared with the average annual budget of the National Water Commission (CONAGUA) in the last ten years; around 40 billion pesos (ANEAS, 2025). This means that we need at least 6.2 times more budget than what is allocated to CONAGUA in a year to be able to attend wastewater treatment in the country under the framework of the new standard. This only considers WWTPs; it should not be forgotten that it is necessary to maintain, rehabilitate, and build new infrastructure (drainage, pumping stations, marginal collectors, hydraulic works for storage, containment and diversion of wastewater, among others) for the collection and conduction of wastewater and, where appropriate, also invest in everything necessary to allocate the treated water for reuse and thus be able to release first-use water for direct human consumption. Plan Mexico foresaw a total investment of 30 885 billion pesos in 2025 for 37 strategic water projects (CONAGUA, 2025). This budget should be increased or at least sustained for a decade.

Abandoned wastewater treatment plants.

 Juan Manuel Morgan-Sagastume

To ensure this, it is necessary to establish the sanitation of the country as a priority strategic project that must transcend six-year terms.

WHAT TO DO? 
Political Times 
It is necessary to eliminate the interference of political elements in the technical decisions required to establish and supervise the sanitation of a locality or a region. Water and its management must be colorless politically, completely neutral. 

Three-year periods in municipal government generate a short-term governmental perspective that hinders the implementation of long-term policies, as is usual with environmental policies. There are situations in which the outgoing government does not provide the incoming one with relevant technical information because they belong to opposing political parties, or the latter repeals what was done by the former. 

Reliable and Affordable Information 
One of the main signs that water management in a region is effective is the availability of reliable, clear, and accessible information in technical, administrative, economic, environmental, and social terms. The lack of information is a major obstacle to promoting public policies that seek to improve water management, as it is related to corruption, inefficiency, impunity, and opacity, as well as very little accountability and the absence of a genuine water culture. 

Research and Education 
It is essential to educate the population, especially children, about the importance of preserving natural resources with a long-term perspective. Information and education programs must be continuous and concerted, and they must integrate and involve all sectors of society. Mexican government should encourage basic and applied research on wastewater treatment and the development of technologies better adapted to the diverse conditions and constraints of the country’s municipalities.

It is necessary to create specialized educational and recreational material appropriate to the geographical reality to raise awareness among the population, in addition to facilitating the change of behavior towards water care as a resource in general, and enabling citizens to appropriate knowledge. This also implies raising awareness in society to accept the need to pay for the provision of water supply and sanitation services.

It is important to consider the specialization and professionalization of the personnel required to operate a WWTP, especially in areas where it is not easy to have people with the appropriate technical training. It is advisable to prioritize those technologies that do not require a high level of specialization for their operation and start-up and, if necessary, to guarantee the continuity of these essential personnel in their employment.

Financial and Tax Support 
We need tariff schemes and programs that allow water operators to self-finance, in addition to effective programs at the three government levels that provide financial support to these entities and guarantee their operation.

Most federal support programs essentially share financial support for construction and investment in or rehabilitation of new infrastructure. However, they do not include financing to cover the costs generated by the maintenance and operation of said infrastructure throughout its useful life. It is common to discover inactive WWTPs, since the necessary economic conditions for their maintenance do not exist. It is crucial to promote appropriate financing directed to the operation and maintenance of treatment plants.

Water Reuse 
The treatment infrastructure should not only be limited to complying with discharge regulations but should also consider the reuse of treated water as a primary objective. This will allow the demand for fresh water to be released in activities that can be carried out with treated water. Promoting agricultural, municipal, home, and industrial reuse is necessary in each population. Studies should be carried out to determine the potential of treated water in populations or regions for proper planning (Morgan-Sagastume et al., 2023). 

Participation of the Private Sector 
One of the dilemmas is to define whether the government should manage the water issue alone or with the help and support of private companies through concessions. To solve this, a fundamental principle is to prevent the imposition of ideologies that aprioristically define what to do, without considering specific aspects of each case. Solutions, both public and private, can operate efficiently if common basic principles of regulation and efficiency are respected, as well as institutional, administrative, operational, and financial conditions.

It is necessary to strengthen the financial situation of public operators, especially in areas or zones of the country with poverty or marginalization, where private interest in investing would be affected by the limited access to financial resources of the inhabitants served. In other words, private initiative alone cannot solve the problem of wastewater treatment in the country; it is necessary for the State to intervene decisively and contemplate the participation of the private sector only as a support under its guidance, coordination and supervision. 

Abandoned wastewater treatment plants.

 Juan Manuel Morgan-Sagastume

Appropriate Selection of Technology 
Technologies are chosen out of habit, previous experience, or according to what the market offers by giving a high specific weight to the decision criterion consisting of the cost of investment, relegating the importance of the cost of operation and maintenance. This approach is not always appropriate, as it can lead to ignoring aspects of the project, as well as the social, economic, or environmental context in which they are implemented. The above, it is clear, is a consequence of the country’s great technological dependence and that, under certain circumstances, leads to falling into unethical commercial interests.

There is no doubt about the effectiveness of most of the technologies available in the market for the wastewater treatment and the production of treated water with the conditions required to comply with current regulations. However, they may require a high amount of electricity, be complicated in terms of maintenance, control and handling of sludge, as well as obtaining spare parts, and require highly trained personnel for their operation. As municipal administrations often face limited resources, the choice of technology is crucial to ensure the sustainability of infrastructure over its lifetime.

Creation of a Highly Specialized Public Technical Body 
It is proposed to create a non-political state or regional public entity or body (apart from the State Water Commissions), which would provide specialized technical support to municipalities, operating agencies, and the private sector, in relation to the selection of technology and to issue its technical opinion on subjects within its competence, such as the design and operation of wastewater treatment and sanitation systems in general. Their help could even extend to providing plant operation services, without replacing the oversight of compliance with discharge specifications that are responsibility of federal and municipal organisms. If this regional technical entity manages treatment plants, it will assume responsibility before the corresponding authority in relation to compliance with current standards and the quality of the water produced, acting as a representative of the municipalities.

This body, among other activities, could create a detailed inventory of the operation of WWTPs in the basin or region, conceptually and specifically define comprehensive projects for the management of the sub-basin and basin with the purpose of reusing treated water, develop a training program to operate and maintain WWTPs, as well as a regional plan to advance in technology appropriate to the area, with the participation of universities and regional institutions dedicated to scientific and technological development and highly qualified human resources (Morgan-Sagastume et al., 2022).

Circular Economy 
Sustainable wastewater treatment technologies are those that use the least amount of energy possible to carry out the processes for which they were created, and at the same time require a minimum number of materials and inputs in general during their construction, stabilization, commissioning, and continuous operation. An intrinsic quality of these technologies is that they should not have a negative effect on the social and natural environment; on the contrary, they will strengthen their development through the production of treated water and the creation of reusable byproducts within the framework of a circular economy (link between water, energy, and food).

In the specific case of wastewater treatment, the circular economy model of products and byproducts is correctly applied, appropriate to what a sustainable WWTP seeks. A WWTP has the capacity to produce high-quality treated water that can be used to return the extracted water to the environment—closing the urban water cycle—or to obtain treated water for use in industrial, agricultural, and municipal activities. Similarly, a WWTP has the capacity to produce byproducts such as biogas, which can be used to generate energy, or sludge that can be used as agricultural fertilizers, to comment on the simplest and most common practices in other countries. There are technologies with the capacity to generate a greater diversity of byproducts that can be used in various economic sectors.

WWTPs can and should be considered as factories or facilities that process wastewater for the generation of treated water with quality and byproducts, no longer as simple water treatment plants, to be able to correctly integrate them into the machinery of a circular economy, following a sustainable approach that fits contemporary trends.

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