Sustainable Management of Groundwater in Mexico: Proceedings of a Workshop (2007)

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An Overview of Mexico’s Water Regime and the Role of Groundwater Felipe Arreguín-Cortés and Mario López-Pérez Comisión Nacional del Agua Mexico has a population of 100 million and faces growing water scarcity. The Comision Nacional del Agua of Mexico (CNA) as the federal authority has the duty to enforce Mexico’s national water law, the “Ley de Aguas Nacionales” (LAN).1 To comply with it the CNA has put in place an infrastructure to monitor the nation’s water cycle and has in progress a wide program for the modernization of water resources management. The recent publications of the water availability of basins and aquifers and the updating of several water regulations are examples of the new integral strategy for water resources management. In this framework it is certain that Mexico’s groundwater constitutes an essential resource for development, especially for the half of its territory that is dominated by arid and semi-arid conditions. It has been estimated that the total groundwater withdrawal of Mexico is 28,000 cubic hectometers per year (hm3/a).2 Irrigation uses more than 70% of that volume, whereas urban and industrial areas consume 26%. More than 102 regional aquifers are over-exploited, with a yearly withdrawal of 5400 hm3/a from storage, resulting in important environmental consequences during the last four decades. Several strategies to overcome these problems, such as water-demand management, water preservation, water-efficient use, social participation, groundwater dams and artificial recharge are considered and carried out. Due to the importance of preserving and increasing subsurface water storage, this article explains the general strategy and points out some of the different options and potentials for groundwater management in Mexico. Introduction Mexico is rich in natural resources. Mexico is privileged in its great ecological diversity. Unfortunately, the development patterns have caused considerable damage to the ecological systems. Environmental protection and rational use of resources are issues of main concern to both the government and society. The Mexican Constitution states that all water is property of the nation: rivers, lakes, springs and groundwater. Within this legal framework the federal government grants concessions to use water. In 1992 the LAN was enacted to regulate water management and mandates a water rights system sustained on a Public Registry of Water Rights. It allows users to sell rights to each other. The reform of the LAN was published in 2004. In this legal framework the major responsibilities of the Comisión Nacional del Agua are to: • Enforce the LAN; 1 Ley de Aguas Nacionales, 1992, Diario Oficial de la Federacion, Mexico City, Mexico. Reglamento de la Ley de Aguas Nacionales, 1994, Diario Oficial de la Federacion, Mexico City, Mexico. 2 Mexico’s water management and data system are in a major state of flux; therefore, it is likely that numbers in this chapter will change over time as data collection systems, access to data, and peer review improve. 13 

• Prepare and update the National Water Program; • Grant permits to withdraw national waters; • Grant permits to discharge wastewater; • Be in charge of the Public Registry of Water Rights; • Assist state and municipal governments in emergencies caused by floods and droughts; and • Foster the development of water supply, sewage and wastewater treatment systems. Population, economic activity and higher growth rates are concentrated in the central, northern and northeastern parts of the country. In these regions, water consumption reaches approximately 2,000 m3/inhabitant/year. This situation is starting to originate supply problems, especially during droughts. Northwest, North and Center 1 951 m3/inh/yr Southeast 14 006 m3/inh/yr Population National average National average Runoff GDP 4 685 m3/inh/yr 4 685 m3/inh/yr 31% 86% 77% 69% 23% 14% Figure 1 Regional rainfall and water use. In terms of the national water balance, the average rainfall is around 772 mm per year which produces approximately 394 billion m3 of runoff. The current hydraulic infrastructure provides storage capacity of approximately 150 billion m3. It is estimated that the country uses 47 billion m3 of surface water per year. The aquifer recharge is estimated at 75 billion m3/year, of which the country uses 28 billion m3/year. In the national water balance, withdrawal is less than the renewable volume. Nevertheless, this global balance does not reveal the critical situation that prevails in arid regions where balance is negative and groundwater reserves are running low. Meanwhile, in the country’s areas with more rain and less development, there is a significant amount of water that is not being used, see Figure 1. The national freshwater withdrawal is approximately 75 billion cubic meters for offstream uses. This volume represents 16% of the national average natural availability (runoff plus aquifer recharge). Nevertheless, in the central, north and northeastern areas, this indicator rises to 44%, which turns water into an element subject to high stress and limits development. 14 

The main offstream use in the country is agriculture because it represents 78% of withdrawal, followed by municipal use with 13%. The country’s industry uses approximately 6.6 billion m3 of freshwater per year and discharges approximately 5.46 billion m3 per year of waste waters. Most surface water bodies in the country receive wastewater discharges, whether household, industrial, agricultural, or livestock wastewater. This has originated varying degrees of pollution, which in some cases limits the direct use of water. Each year an average of 24 cyclonic events happen in the oceans that surround the country. Of these events two or three enter into the territory and cause severe damage. Intense rains and floods, as well as landslides also result from the storms originated during the rainy season. The problem of aquifer overdrafting in the country is worsening. In 1975, 32 aquifers were overdrafted. This number rose to 36 in 1981, to 80 in 1985 and to 102 in 2004 (see Figure 2). 102 out of 654 aquifers are overexploited. 50% of the abstracted groundwater is withdrawn from overexploited aquifers. Overexploited aquifer Salt intrusion aquifer Overexploited with salt intrusion aquifer Administrative regions limit Figure 2 Aquifer overexploitation3 Water Monitoring Systematic meteorological and hydrological observations were started in Mexico in 1877 and 1921, respectively. Today the CNA is the federal authority responsible for carrying out the hydrological cycle observation, in order to assess water quantity and quality, and its spatial and time distribution throughout Mexico, from the upper air to underground sources, and from the mountains to the mouths of the rivers. The Servicio Meteorologico Nacional (SMN) initiated activities on March 6, 1877, with 10 synoptic ground stations. By 1900, the NMS had 31 State Offices and 18 synoptic 3 Mexico, Comisión Nacional del Agua (CNA), http://www.cna.gob.mx/eCNA/Espaniol/Directorio/ 15 

ground stations, transmitting data by telegraph to NMS headquarters in Mexico City. Recently, modernization actions have been achieved with NMS as a part of CNA support. The plan includes the goals of having Mexico meet minimum data collection standards as recommended by the World Meteorological Organization (WMO) in both ground stations and upper air stations. During these years, several actions have been implemented in order to increase the amount and quality of data collected, to have computers perform as much processing as possible and to increase in both quantity and quality the forecasting products utilizing modern technologies. The meteorological radar network constituted by 12 C-Band Doppler Radars have a direct readout ground stations to receive GOES and TIROS satellite imagery in real time. The meteorological network also includes 74 automatic ground stations with modern Data Collection Platforms, and 15 fully automated upper air stations with GPS capabilities in operation, in addition to 79 manual analog instrumented ground stations. The climatological network consists of 3200 stations equipped with at least a rain gauge (see Figure 3). In about 2700 stations there is an evaporation pan, and around 250 of them have an analog rainfall recorder, and 91 digital tipping bucket type rain gauges were acquired in 2002. The relative humidity is measured in approximately 150 stations. Figure 3 Existing conventional climatological stations. The hydrometric (river gauge) network includes 818 river gauge stations, almost all on rivers which have more than 1000 km2 of catchment basin area. At 113 of these stations, suspended sediments are also monitored, while records are kept for 182 dam reservoirs. There are 54 Data Collection Platforms (DCP) which transmit data by satellite; all of them are equipped with instruments to determine river flow and rainfall, and some have in addition meteorological instruments to register barometric pressure, wind velocity and direction, relative humidity, temperature and solar radiation. Data from 800 16 

climatological stations, 22 hydrometric stations, 128 DCP´s, and about 70 rain gauges in Mexico City, are transmitted to the CNA on a daily basis (See Figure 4). NWS Telecommunications Gateway / World Meteorological Center Washington, D.C. • The World Area Forecast System (WAFS) • The Regional Main Telecommunication Network (RMTN-IV) pr od uc t ta s da NMS National Center for NMS National Center for Meteorological Telecommunications Weather Forecast Figure 4 Servicio Meteorologico Nacional and the Global Telecommunications Systems. More recently, CNA has launched an effort to revise the complete operation of the hydrological cycle observation networks, and in what relates to the hydrometric and climatological networks, there is a new task oriented to define National Reference Hydrometric and Climatological Networks, which by definition are constituted by the Level II stations which represent those sites having more than 30 years of data, where the data are not influenced by urban “heat-island” effect, and the data are of good quality. Such long-term data series are especially valuable for detecting possible changes in climatology due to greenhouse gas forcing, and in-depth climatic studies at the Nation’s level. This information has allowed the CNA to start a huge process to comply with the LAN to enact the water availability of river basins and aquifers. On October 15, 2003, the water balance of a river basin, Lerma Chapala, was issued for the first time in Mexico’s history. Seven more major basin balances are now in preparation. Many of them are to update water regulations that were published during the first part of the last century. The collection and analysis of these data are critical steps to the enhancement of our understanding of Mexico’s aquifers and will be useful for similar analyses in the future. 17 

There are piezometric data on about 258 aquifers. However, the main monitoring system only covers 144 aquifers, including 102 overexploited aquifers, 30 in fragile equilibrium and the remaining 14 with important water resources still underexploited (see Figure 5). The main monitoring system mentioned above comprises, among others, the main aquifers of the water basins of Lerma-Chapala, Bravo River, Valley of México, Sonora and Baja California States. Groundwater Users Committees (COTAS) for management purposes have been constituted for 57 aquifers out of those 144. By year 2003, the monitoring networks of 104 aquifers have been reactivated, updating data and monitoring activities; all data have been retrieved, validated and stored at the Groundwater Geographic Information Management System. Groundwater Monitoring Networks actual networks networks reinitiated 2003 Monitoring Wells: 4,190 in operation Figure 5 Groundwater monitoring network. The water quality monitoring activities have been carried out in Mexico since 1974. The program has the following components: (a) the National Water Quality Monitoring Network; (b) the National Laboratory Network for Water Analysis; and (c) the Water Quality National Information System (SNICA) that integrates some of the existing databases and information sources. The Primary Network provides nation-wide, long-term information on the status and trends of the nation’s surface, coastal and groundwater resources, which consists of 366 sampling stations, distributed as follows: 205 surface water sampling stations, 117 groundwater sampling stations, and 44 coastal water sampling stations. A fixed-site network is not sufficiently flexible or cost-effective to provide information for regulatory purposes. The objective of the Secondary Network is to provide information for the purposes of Water Rights Administration. Currently, the Secondary Network is made up of 289 stations. A pilot study is now underway in the Balsas river 18 

basin with the objective of validating the sampling and siting methodology for this Secondary Network. Looking only at the surface water components of the Primary and Secondary Networks, they cover 194 water bodies, including the 15 basins that receive the largest pollution loads in the country. At the same time, the Primary Network includes 31, and the Secondary Network 26 of the 32 largest rivers in Mexico. Groundwater management Groundwater constitutes an essential resource for development in Mexico, because more than half of Mexico’s territory is arid and semi-arid. Furthermore, Mexico’s water supply depends heavily on groundwater resources. Current total groundwater withdrawal is 28 billion cubic meters per year (m3/yr). More than one third of the total consumptive use of water comes from current groundwater withdrawals. Groundwater dependence is highest in the urban/domestic sectors, which obtain more than 70% of their water requirements from this source. About 75 million people (55 million people living in the largest urban centers, and 80% of rural population, 20 million) depend on groundwater for their water supply. Agriculture uses 70% of the total volume; cities consume 23%; industries use 5%, and rural population represent 2%. Groundwater is also the only water source for most industrial development in northern and central Mexico. There is an existing inventory of about 130,000 wells with significant pumping capacity, 80,000 of which are for irrigation purposes and 15,000 for municipal and industrial supply. Even though agricultural irrigation relies more on surface water, it is still the major groundwater user. There are areas in the northern, northwestern and central Mexico where irrigation depends almost entirely on groundwater. About 80,000 wells, mostly private, are being used to irrigate more than 2 million hectares of land, i.e., more than one third of the total irrigated land in the country (6 million ha). According to the Mexican National Electricity Commission, in 2000 groundwater irrigated agriculture consumed 7815 GWh equivalent to 6.2% of the total national electricity consumption. The national groundwater balance is positive on an overall basis since withdrawal represents only 70% of the natural recharge. However, this positive balance hides critical aquifer overexploitation in the central and northern regions of the country. The National Water Plan of 1975 already underlined the overexploitation of 32 aquifers. At present, it is estimated that about 102 of Mexico's 258 main aquifer units located mainly in the northwestern, northern and central regions (in 16 states), are currently being overdrawn. What makes it even worse is that the 102 overexploited aquifers are directly related to the most important industrial and urban centers, turning water resources availability into a factor limiting the sustainable development of the region. In order to cope with the main groundwater problems from a legal and technical basis, many studies were updated, including GIS updating, and a general strategy was developed. Article 22 of the LAN states that water use permission is granted only when availability exists. The law also underlines the need to have standards to determine water availability (article 37 and transitory 13 of the LAN Regulation). The standard to determine the water availability in basins and aquifer units was issued on April 17, 2002. 19 

The standard as a national regulation is mandatory and establishes the minimum requirements to determine the mean annual groundwater available. In 2003, The water availability of 202 aquifer units was published for the first time in the water history of Mexico (See Figure 6). The 202 acuifers published represent the 85 % of the national groundwater use Figure 6 Groundwater availability published on January 31st and December 29th of 2003.4 In parallel to updating the groundwater availability information already issued, the next step is to publish the data on transborder and transregional aquifers and special cases. A media campaign was launched in order to spread the information and benefits that this publication brings to the users, governments and to the society in general. The purpose of the publication extends beyond the provision of information in order to grant water use permits. It also provides the basis for updating, establishing, or suppressing water regulations like water reserves, water prohibitions and sets of water management rules. Also, this process is in progress in regions of Mexico where the overexploitation is most severe. Traditionally, some of the groundwater balances estimate in a simple way some of the parameters of the mass equation, due to the lack of information. Today the CNA is developing studies with a different approach using the Net Groundwater Use (Sebal) method. This method, developed in the Netherlands, determines the up-to-date accurate evapotranspiration parameter with the aid of the temperature measured by remote sensing. For different purposes and places around the world this method has been applied successfully. In Mexico the first exercise was in the Lerma Chapala Basin. These studies will help to make the water availability publications among many other possible applications more accurate. Another kind of approach to assess the aquifer restoration and protection is the vulnerability determination. The characterization and monitoring help to determine, for 4 Mexico, Comisión Nacional del Agua (CNA), http://www.cna.gob.mx/eCNA/Espaniol/Directorio/ 20 

each aquifer unit, the pollution risk, the protection measures, the suitable land use and the need for specific studies. Again, as with the Sebal method and the traditional water availability process the results and basic data are GIS-based. Current water use conditions threaten the progress and development in Mexico, with serious consequences to the national economy. It is clear that sustainable development in Mexico’s arid and semiarid regions will depend heavily on increasing water availability by: a) management of water demand, b) water reuse, and c) artificial recharge. These are the cornerstones of Mexico’s strategy with a sound social participation. In the past, a nation’s response to an increasing water demand was to satisfy it with a larger supply through new water projects. Now the approach has shifted to an integrated strategy that emphasizes water demand management involving all users. The National Water Law promotes social participation through stakeholder councils and committees, to implement programs of water preservation. Water demand management among different users deserves special care. Campaigns on efficient water use and penalties for water law violations have been implemented. Water recycling and reuse of treated wastewater have been tax-promoted among industrial users for ad hoc activities. Modern irrigation projects, more efficient agricultural practices, and new technologies (e.g. plasticulture) have also been implemented to reduce water consumption. The concept of the water market is being promoted through the exchange of existing irrigation water rights to satisfy demand in cities where water availability is not sufficient. There are several other releasing mechanisms. Where urban areas displace agricultural lands, water rights are exchanged through transference from original farmers to industrial users and city agencies. Some other users, who do not need potable water transfer their water rights and receive in turn an equal amount of treated wastewater. Rights owners who implement programs to use less water by enhancement of both crop production and well efficiency are assessed. The CNA has recently devoted special attention to monitoring, evaluating, modeling, and sustainably developing groundwater resources, especially to stabilize over-exploited aquifers. Artificial recharge has also been considered in order to enhance groundwater storage. Water availability in Mexican arid lands is insufficient. Stormy events generate extraordinary runoff that could be used for artificial recharge modifying riverbeds and infiltration basins. Several basins along the Pacific Coast prone to hurricanes could benefit from it. A project underway in Baja, California considers a combination of artificial recharge and the construction of a sub-surface dam to increase groundwater storage, allowing a flexible pumping with no risk of seawater intrusion. As a means of increasing water availability, isolated artificial recharge projects have been conducted in Mexico but widespread use of recharge practices has been delayed due to 21 

technical and economic difficulties. In addition, the legal framework is another issue to be considered, since the Mexican water regulations establish the need for permission for both artificial recharge and subsurface water disposal. Since there is no Mexican Official Standard (MOS) on groundwater recharge a project developed last year is under revision. The main considerations are: a) compliance should not be so difficult that it discourages artificial recharge projects; b) it should not be so weak that it threatens public health. The goal of a potential MOS on groundwater recharge would be to protect aquifer water quality and prevent public health damage. The project establishes guidelines on quality of effluents being recharged, instead of regulating treatment systems or methods for artificial recharge. It establishes quality requirements to be met depending on recharge method (from surface or from subsurface) and potential use of recovered water. It also defines minimal distances between recharge facilities and closest potable wells. If reclaimed water is intended for potable uses, the standard defines strict water quality criteria and considers subsurface natural treatment as a complementary protection. If final use is not for human consumption, natural treatment is considered to relax water quality requirements for recharge, lowering costs on previous treatment. The subsurface environment as a natural treatment system is considered in the Mexican standard. There is a tendency to use it through a suitable combination of pre-treatment, natural treatment, and post-treatment; according to recharge methodology and final use of recovered water. Artificial recharge using wastewater is recommended when recovered water is not used for potable purposes. However, extreme care must be taken when wastewater recharge is intended for human consumption. In such a case, additional issues are required: basic studies, tertiary/advanced pretreatment, careful monitoring, suitable distance among recharge sites and recovering wells, etc. Sooner or later, wastewater recharge will be necessary in some northern Mexican basins, where no other reliable options exist. It is clear that artificial recharge depends on: a) sufficient water for recharging purposes; b) good water quality to prevent impairment of native groundwater or feasibility of artificial/natural pretreatment to avoid contamination; c) land availability for recharging facilities; and d) prompt and easy recovery of recharged water. Artificial recharge projects involve high costs. Large recharge projects to create or increase available water storage are only feasible if government and organized users support them. This possibility is being addressed by local Groundwater Users Committees (COTAS) for over-exploited aquifers, as a strategy for sustainable management. Wastewater from urban and industrial zones constitutes an enormous potential supply for artificial recharge mainly because of its increasing volume and its perennial nature. Wastewater quality, however, represents concerns: a) treatment is required to prevent contaminant risks and damages to public health, especially when recharged water is intended for human consumption; b) wastewater irrigation is a common practice in Mexico. There is an enormous recharging potential in the Valley of Mexico Basin due to 22 

the great effluent flow rate (40 m3/s). A large-scale wastewater treatment for reclamation and artificial recharge is attractive but care must be taken to avoid polluting potable water-supplying wells. Feasibility of joint management involving dams and aquifers has being assessed in humid and semi-humid regions, where exceeding surface water can be used for artificial recharge. Some of the recharge methods considered comprises surface (infiltration basins and river beds) and subsurface application. Surface recharge has greater possibilities in sparsely populated zones, whereas it is difficult to achieve in populated cities, where land availability is a major problem. Construction of wells to inject water through saturated/unsaturated zones is becoming popular in those cities. It is also possible to collect rainwater for recharging purposes in the same regions. Some examples include the urban and industrial developments at the Metropolitan Zone of Mexico City, other important cities and Comarca Lagunera. A recent study on water reserve in the main Mexican aquifers included an estimation of its total size and determinations of storage releases from over-exploitation. Results showed that during the last 40 years, 60,000 Mm3 were taken from groundwater storage nationwide by aquifer over-exploitation, whereas current release from storage is 5400 Mm3/a. Most available groundwater has been stored within the first 400 m below the ground surface, in the most permeable aquifers where renovation is more dynamic. There, groundwater has the best quality, and it is economically available. It is considered that there is an important storage up to a reference depth of 400 m. Results on remaining water reserve, however, are being carefully considered. The biggest environmental impact was generated during the first decades of over- exploitation (1960’s through 80’s) resulting in disappearing springs, desiccation of lakes and wetlands, declining base flow, and damage to ecosystems and natural flora. Common related effects seen in Mexico were: declining well production, higher pumping costs, land subsidence and fracturing, groundwater contamination, salt water intrusion, and strong competition among users. Conclusions Mexico has a long tradition of measuring the variables of the water cycle and determining the state of our water resources in terms of quantity and quality as well as in space and time. Development and waste use practices have brought Mexico to a point where the water resources cannot sustain these patterns. The CNA is encouraged and has the legal framework to reverse the situation. Science provides the foundation for the necessary management decisions. The first step is to publish groundwater availability, update regulations, and apply new and useful methods and techniques for water management featuring user participation. In this context, it is certain that Mexico’s groundwater reserve is a strategic and valuable resource, especially in arid and semiarid regions. Its national magnitude, permanence and overall spatial distribution compensate scarcity and temporal variations in precipitation runoff and aquifer recharge and that it should be handled with great care. It confers a greater flexibility on integrated water management. 23 

However, overexploitation is permanently generating several pernicious effects resulting in a non-sustainable destructive condition in the long run. Controlled temporal over- exploitation is possible and even recommended, only when affordable in terms of costs and benefits. Rational management must consider that groundwater reserve is large but it is not being completely replenished. Additionally, its exploitation faces physical, economical and environmental limitations, and determinations of its magnitude decrease in accuracy with depth. The studies show that it will become significant with severe droughts resulting from global climatic changes. It is urgent to implement management strategies to increase and preserve groundwater reserve for elementary uses (e.g.: drinking). Artificial recharge and groundwater dams should be included among the strategies. Executive studies and pilot projects both on artificial recharge and groundwater dams are strongly recommended. Possibilities on wastewater reclamation through artificial recharge and further recovery for potable purposes should be investigated, especially in cases of scarcity and lack of complementary supply. Another set of critical issues to be considered in the integral strategy for a sustainable groundwater management include: • an adequate monitoring system for groundwater resources management in quantity and quality; • in-depth quantitative studies supported by mathematical models; • a groundwater database linked to an information management system to process groundwater-related data to aid in assessments and modeling, and in any decision- making process; • potential approaches to groundwater resource development and protection supported by specialized studies dealing with environmental costs of groundwater mining or overexploitation, socioeconomic aspects of aquifer-stabilization programs, analyses of demand management for groundwater conservation, and environmental impact of groundwater resource degradation by agricultural, industrial and urban pollutants; • special studies directed to define feasible proposals, with action programs, financial and economical analyses, and implementation instruments; and • Groundwater Management Plans and Aquifer Regulations prepared with a broad and sound social participation assured by the COTAS. 24 

References Arreguín-Cortés Felipe and Chávez-Guillén Rubén, CNA. 2002. State of the art of artificial recharge through well injection in Mexico, Seminar/workshop “Recharge enhancement and sub-surface water storage, a promising option to cope with climate variability.” Wageningen, the Netherlands. Arreguin-Cortés Felipe and Trueba-López Venancio, CNA. 2003. Improvement and Assessment of Water Quantity and Quality Monitoring Networks in Mexico. Seminar/workshop Salamanca, Guanajuato, México. CNA. 2001. Programa Nacional Hidráulico 2001 – 2006. Plan Nacional de Desarrollo 2001 2006. Comisión Nacional del Agua. SEMARNAT. CNA. 2002. Revisión de Sitios de la Red Primaria – Red Nacional de Monitoreo de Calidad del Agua. Informe OMM/PROMMA No. 114. Organización Meteorológica Mundial. Comisión Nacional del Agua. CNA. 2002. Hacia un Programa de Modernización de Monitoreo Hidroclimatológico en México. Compilación y síntesis de las Recomendaciones para el Fortalecimiento y la Modernización de las actividades de Hidrología y Climatología Operativa. Informe OMM/PROMMA No. 115. Organización Meteorológica Mundial. Comisión Nacional del Agua. CNA. 2002. Evaluación Técnica 2002 del PROMMA. Informe Final; 5ª Misión de Evaluación OMM/PROMMA. Informe OMM/PROMMA No. 130. Organización Meteorológica Mundial. Comisión Nacional del Agua. CNA. 2002. Rediseño de redes de Monitoreo Hidroclimatológico en Cuencas Prioritarias de México – Síntesis. Informe OMM/PROMMA No. 147-00. Organización Meteorológica Mundial. Comisión Nacional del Agua. Ley de Aguas Nacionales, 1992, Diario Oficial de la Federacion, Mexico City, Mexico. Reglamento de la Ley de Aguas Nacionales, 1994, Diario Oficial de la Federacion, Mexico City, Mexico. 25