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(Ley Federal sobre Metrología y Normalización) and its Regulation. The emissions not regulatedby official Mexican standards or that are exempt from measurement can be estimatedthrough commonly used methodologies, such as the application of emissionfactors, estimation from historical data, balance of materials, engineering calculations,or mathematic models.Finally, it should be mentioned that the information provided by interested partiesregarding emissions and transfer of contaminates will be available to the public in generalonce the RETC is fully consolidated. Such information will consist of the name of theestablishment, its emissions and transfers of substances and contaminants and its geographiclocation.4.5. Official Mexican Standards (normas oficiales mexicanas, NOMs)Currently there are approximately 30 NOMs related to air pollution. Several of them referto methods of measurement to determine the concentration of certain types of air emissions.Others establish the maximum permissible levels of air emissions of various substances,such as sulfur, solid particulates from fixed sources engaged in the manufactureof cement and volatile organic compounds coming from the process of water-oil separationin oil refineries.5. Legal Framework Governing Water in Mexico297Environmental LawThe National Waters Law (Ley de Aguas Nacionales, LAN) and the Regulation of theNational Waters Law (Reglamento de la Ley de Aguas Nacionales) are the laws governingthis area, and the National Water Commission (Comisión Nacional de Agua, CONAGUA),a semi-independent administrative agency of SEMARNAT, is the responsible authorityregarding national waters.Although CONAGUA is a semi-independent administrative agency of SEMARNAT, in realityit is almost totally autonomous. This agency is responsible for all aspects of nationalwaters, from their supply to the oversight of the discharge of wastewater. SEMARNAT hasjurisdiction over the application of the laws in relation to Mexican marine waters.It should be mentioned, however, that the LGEEPA includes a chapter on the preventionand control of the contamination of water and of aquatic ecosystems, and that SEMARNATin theory has powers in relation to the ecological aspects of national waters.In Mexico, Article 27 of the Federal Constitution makes a broad classification of thewaters owned by the nation, and as a result in order to make use of such national watersit is necessary to have a concession and to pay the fees for the concessioned water. Furthermore,a discharge permit that establishes the conditions for discharge of the watercovered by the concession title is required.