The Social Sciences have contributed to the study of Sustainable Development from economic analysis, political, social, psychological and media on the consumption of natural resources in reference to their availability, extraction, and distribution, supply and recycling. In this sense, the objective of this work is to outline eight areas for the analysis of water issues. The relationship between availability and consumption of water belonging to the public supply network is described to establish a system of water tariffs set to situational water areas. In the case of water consumption rates, they seem to be due to public policies "clientelistic" that make it unfair charging system, subsidies, penalties, trading and transparency. The prevalence of clientelist system encourages water and increases the problems of conflicts between citizens and government through neighborhood networks against administrative authorities. In the future, the trend of availability and water consumption seems to outline a situation of extreme scarcity in which conflicts over water supply will be an indicator to explain economic crisis, political, social and individual. The discussions of water issues that prevent humanity develop sustainably contribute in building a public agenda water.

Global to local water situational trends are presented in order to project the corresponding water sustainability. In this sense, public policies are essential to establish the costes of water supply. However, citizen, community and neighbourhood participation is also essential in the establishment of unit water prices. 

Thus, at the global level, water sustainability is determined by public policies that encourage water savings through international tariff standards. The price of water would be a consequence of international agreements in which the signatory countries commit to reduce their agricultural, industrial and commercial processes. The unit cost would be defined by the level of availability per capita. A larger amount of water for each person would imply a standard cost for the claimant. Consumption above a threshold would exponentially increase the unit price. Globally, costs would be reduced and profits would increase substantially. However, presidents or ministers cannot make global decisions without compromising local development.

In this sense, at the continental level, the relationship between the industrial north and the agricultural south, trade between economic blocs, has a direct impact on the financial and migratory flows that must be considered in the equation of a public policy for water sustainability. At the level of the continents, the establishment of a system of charging for water service is more feasible if we consider the trade agreements between the members of the economic blocs. As a geopolitical group, a public tariff policy would be geared towards subsidizing rich citizens for the subsistence of poor residents. It is a tariff system in which those with greater purchasing power pay a standard tariff that includes financing for those who live in exclusion, marginalization or vulnerability. However, localisms continue to have a specific weight when establishing standard rates and therefore it is necessary to review the national level to clarify the factors that impede sustainability at the continental level.

One cause of economic blocs has been nationalism. From the nationalist conflicts that led Europe to create a common market, to the regionalisms that today promote the collapse of monarchies in Africa and the Middle East, local ideologies have determined the future of societies. In Mexico, conflicts over the right to water have been mitigated by centralist and federalist public policies that justify the extraction and distribution from one basin to another.  The State, through the estimates of the Ministry of Finance and Public Credit (SHCP), the Bank of Mexico (WB) and the National Water Commission (CONAGUA), has established public policies aimed at economic growth rather than sustainable development. The State ignored the water rights and assets of rural communities and urban neighborhoods. In this sense, each unit of water has a different and inequitable price. Water is cheap for those who have greater purchasing power and consume more. On the other hand, groups that save water, despite being unemployed or underemployed, pay five times its real cost. However, national water policy is diversified at the state level.

In a federalist country, state governments are a counterweight to the omnipresence of the executive. A president's initiative can be amended by the upper and lower house, the state congress, and the governor. If we add to this the altitude at which rural communities and urban neighborhoods live, we have that states would legislate a differential rate system for each entity. For this reason, the state's water sustainability would have its main obstacle in the finances of the states. Often, state governments spend more than they receive from the federation. This encourages national and local operating bodies to seek agreements to build a subsidy system that benefits users with low prices. The result is a public action organized for collection but disorganized for supply. Without fail, bills are distributed to users but water service is intermittent. For this reason, state water sustainability benefits cities to the detriment of rural areas. 

The Metropolitan Area of the Valley of Mexico (ZMVM) is a paradigmatic case of the water trend in the history of humanity. The MVMA has always been a repository of rainfall, seepage and discharge from rivers and lagoons. It could be said that since the founding of the Valley of Mexico there was an obvious overload. Over the centuries and cultures, the basin has been emptied. It is estimated that the current extraction trend would last for about two or three decades to compromise its structure. This geographical complexity is no less than the socio-political complexity. The Valley of Mexico is administered by three entities with their respective congresses. A metropolitan water policy would be defined by representatives of different localities with different needs, expectations and consumption capacities. However, the Mexican Political System (SPM) is characterized by homogenizing the demands of the people and the corresponding offers. On the basis of this structural political feature, a water policy price system is in reality a system of concessions, subsidies and forgiveness. It is a public policy that does not need to be legislated in order to be implemented. At election time, the efficiency of the political system uses the drinking water service as its instrument for promoting, defining and electing candidates and representatives. In this way, metropolitan water sustainability is discretionary, proselytizing and clientelistic. Consequently, at the delegation level, corruption, nepotism and clientelism are its main components.

A consequence of the complexity of the Valley of Mexico is its delegational and municipal demarcations. The diversity of factors that influence metropolitan water sustainability also has an impact on water sustainability at the delegation level. However, delegations are grouped into two groups: inclusive and exclusionary. The former have a low population density and high incomes that would allow them to pay for an exponential increase in rates. The latter are overcrowded, unemployed or underemployed with insufficient income to afford a minimal variation in the unit price of water. In the case of the Iztapalapa delegation, we should add the altitude and the corruption in which the neighborhoods with the greatest shortages and unhealthiness live. It is a delegation in which various factors converge and brings its inhabitants closer to a water crisis. This situation favors the emergence of the location or intentions-actions of non-conformity, protest, confrontation or boycott aimed at obtaining a greater amount of water. Thus, water sustainability in Iztapalapa would require rates adjusted to the uses and customs of its inhabitants who fight corruption but at the same time accept clientelism. In this sense, family-residential lifestyles complement their collective mobilizations.

In the residential environment, water scarcity is the main trend that would lead families to hoard, dosage and pseudo-repair leaks. Indeed, a tariff system in line with austerity strategies would imply consumption thresholds determined by the number of residents, their economic activities and types of recreation. At the level of households, water sustainability means a subsidized payment to those who save water and an exponential price to those who waste or hoard it. Consumption skills and pseudo-leak repair would imply a smaller subsidy that would fit a standard price considering the future trend. 

Finally, the water trends presented project future scenarios in which urban density is a global, national and local problem that affects water sustainability. In other words, the expected per capita availability for the coming years is a consequence of public policies that seek to curb the water trend rather than make it sustainable. In this sense, the disappearance of standard, subsidized, situational, interval or tariff threshold systems is predictable. Instead, a new pricing system will need to be implemented to address structural flaws. It is a tariff system determined by global to local water contingencies. 

Regarding environmental problems, the social sciences propose the following approaches:

Regional-Community Studies. Water issues, related to solidarity in times of scarcity and festivity in times of plenty, are felt as elements of the community. Community self-management is the main manifestation of global water imbalance with local scarcity effects. That is to say, the lakes, rivers, lagoons, aquifers or glaciers that historically belong to ethnic communities, when overexploited by the cities, propitiate mobilizations in defense of the community heritage for its preservation. In this sense, Sustainable Development is comparable to the self-management of communities due to their historical right to water as their subsistence heritage (Breña, 2004: 40). 

Legal Studies. The main problem is the defense of the rights to access and consumption of water. In other words, the aquifers, lakes and rivers that belonged to ethnic groups were expropriated by their governments and redistributed to areas of industrial or agricultural economic development (Morales, Rodríguez and González, 2007: 225). Once again, Sustainable Development is the solution to the problem of the legal recognition of peoples to their self-determination. Sustainable Development is conceived as a document, treaty or agreement in which the laws or principles of the relative autonomy of peoples, groups or human settlements are embodied. Institutions such as the secretariats of the environment or the human rights commissions act as zealous watchdogs of the agreements that the states have signed to control their abuses over the communities and the resources that correspond to them (Hernández, 2004: 330). 

Economic and Social Studies. Water problems are studied in relation to human development indices. Ideal human development is related to the optimization of water resources. In contrast, impoverished human development is linked to scarcity, corruption, leakage, and waste. From the economic sciences, the dilemma of the capitalization of natural resources versus their conservation is posed. Faced with such a dilemma, Sustainable Development is proposed instead of economic growth and the preservation of the environment (Corral, 2010: 123). Water economic approaches establish water-saving mechanisms based on tariff systems. The price of drinking water services is established by minimizing or maximizing the relationships between services, their costs and their benefits in exchange situations (Dávila and Constantino, 2007a: 185). In this sense, an increase in unit water prices has an impact on the reduction of consumption and distributive equity. Precisely, in the ZUPs subsidies are established, while in the ZUC incentives are established for the optimization and treatment and reuse of water. Economic organizations such as the International Monetary Fund or the World Bank measure sustainable development based on indices specialized in establishing the causal relationship between per capita income and health, work, education, food, quality of life or subjective well-being (Goicoechea, 2007: 265). 

Political-Social Studies. The impact of the scarcity of water resources on the central and peripheral areas of public investment decisions is the problem that frames the study of conflicts between citizens and their authorities. There are two water problems: equity and service financing (Dávila and Constantino, 2007b: 160). Faced with the demands of the citizenry, the rulers offer greater coverage by overexploiting aquifers and filtering wastewater (Goicoechea, 2004: 125). It is a public policy guided by sustainable planning; comprehensive, efficient, equitable and inclusive (Morales and Rodríguez, 2007a: 290). Demands for water resources are manifested in sit-ins, rallies, marches, propaganda and confrontations with the police. Citizen mobilizations are analysed as "clienteles", a mechanism of political electoral control by parties over excluded groups (Cunill, 1991). Faced with such problems, solutions are studied that revolve around an electoral reform in which the rulers offer greater transparency in the management of resources in exchange for greater citizen participation in elections and accountability (Chávez, 2004: 135; López, 2004: 107). In this sense, the legislative branch and its initiatives that allow the direct participation of the majorities and especially the minorities, the main victims of economic growth at the expense of overexploitation and scarcity of resources, in investment and financing decisions for personal and group development are studied. Sustainable Development is the product of debates between citizens and the state, it is an agreement in which both political figures agree on the rational, planned and moderate exploitation of water resources.

Sociological Studies. Water problems focus on environmental uncertainty. The environment is considered as a set of immeasurable, unpredictable and uncontrollable variables that exhibits humanity and its societies as part of the process of evolution and transformation of nature. In other words, nature has gone through different evolutionary stages and the climate change that we are experiencing and suffering today is just one more stage in the development of the Earth. At that stage, humans will become extinct unless their systems can slow the effects of climate change or adapt their descendants to the environmental contingency. The sociological sciences posit risk societies in which technological advances such as nuclear power plants, air transport or water infrastructure can collapse at any time and thus compromise the growth of current and future generations (Ramos and Lorda, 2004: 70). Sustainable Development is a context of certainty in times of risk, a context of security in times of uncertainty, a context of trust in times of negligence and corruption.

Psychological Studies. Water problems consist of the impact of water availability on perceptions, emotions, attitudes, motives, intentions, skills, competencies and behaviors (Corral, 2010: 156). Scarcity, shortages, hoarding or unhealthiness have a direct effect on water saving. This effect is also mediated by cognitive variables (Corral & Pinheiro, 2004). Psychologists carry out the reliability and validity of instruments that measure these variables in order to relate them to other situational, demographic, educational, or geospatial variables. Sustainable Development consists of the adoption of anti- or pro-environmental cognitive and behavioral styles. 

Public policies determine global, continental, national, state, metropolitan, delegational, residential, and prospective water sustainability. Public policies try to organize the determinants of water availability based on tariff parameters for the financing of water sustainability. An increase in the unit price of water service has a direct, positive and significant impact on its optimization and savings. 

In this way, public policies have created seven tariff systems to guarantee water sustainability.

Fee per standard. The rate per unit of water is independent of the amount of water consumed. 

Volume fee. The unit price of water depends on how much is used. It increases or decreases based on government discretion.

Rate per situation. The rate per unit of water increases your cost during the day and decreases your cost at night. During the summer season its cost increases and during the rainy season its unit price decreases. It is equitable and saves the cost of pumping and purification.

Interval rate. The unit price of water increases according to the volume consumed. From the consumption intervals, prices are applied that increase as consumption exceeds the permitted thresholds. 

Threshold fees. The unit price of water is constant as long as it does not exceed the comfort threshold. Once the allocated consumption has been exceeded, an increment is applied, linear, logarithmic, exponential or logistical. 

Self-financing fee. The unit cost of the service is established based on family income and a comfort threshold. Once the allowed limit is exceeded, the cost increases for each extra cubic volume. 

Subsidy fee. The unit cost of drinking water service involves a standard or tiered fee and a subsidy based on a comfort threshold. 

Global Scope 

Global water situations are significantly related to population size, distribution, and density (see Table 1). In 1960 the Club of Rome, based on the observations of economist David Ricardo made in the previous century, was the first environmental scientific group to demonstrate a direct association between population growth and decrease in hydropower resources. However, this distributive law was used by governments to hold individuals accountable around their exponential and indiscriminate reproduction. States considered that individuals should reproduce as a function of economic growth and technological advances (Leff, 2002: 2004). The Cold War seemed to have a greater impact on the overpopulation of developed and peripheral countries, thus initiating the imbalance between the availability of resources and the needs of the predecessor, current and succeeding generations (Guillén, 2007). In fact, the Club of Rome had only established the inverse relationship between the quantity of natural resources, their consumption and their renewal, but did not consider in its diagnoses the symbolic determinants such as; norms, values and beliefs that prevent humanity from developing sustainably. 

However, in its 2010 report, the European Water Statistics Agency (AQUASTAT) warns of a historical trend in which the availability of resources descriases as a function of population growth, urban needs, capacities and consumption expectations. 

Table 1. Global scope of the water situation

Fuente: AQUASTAT (2010), FAO (2010), OMS (2010), ONU (2010), UNICEF (2010) the USCB (2010)

Indeed, with migration from the countryside to the cities, lifestyles changed. The increase in rural populations, urban density and economic growth determined new norms, values and beliefs about nature that considered it a set of inexhaustible and immeasurable resources. Currently, the trend seems to be towards a direction in which manufacturing industrialization is no longer responsible for the imbalance between the availability of resources and the population rate. Now that the population has reduced its trend, its needs, capacities and consumption expectations seem to be the causes of the highest water consumption in history. Thus, agriculture and industry are the biggest water demanders and underground aquifers are the biggest suppliers. 

The global water situation seems to be determined by economic growth which, once basic needs were met, increased consumption capacities and expectations. Despite the fact that the population trend has been reduced, inequalities between developed countries and emerging nations seem to determine the drastic decrease in water per capita 

In this sense, global water sustainability would be indicated by global policies that are based on the establishment of the unit cost of water based on population growth, distribution, scarcity, availability, use, exclusion and investment. If this is the global trend, then you would have to look at the data for the continents to corroborate this trend.

Continental Scope 

The continental water situation is indicated by contradictory differences between capital, availability, extraction, supply, and migration (see Table 2). There is an inverse relationship between the water capital of each continent and per capita availability. While the former remains constant, the latter has shown an accelerated decline in recent years. This scenario contrasts with the levels of extraction in which the basins are highly overexploited, but the supply presents a slowing supply. Even the migratory factor from continents with low water availability to continents with medium availability substantially decreases the amount per capita. In this sense, the continental water situation would be determined by migratory flows, which in turn are determined by financial flows. In other words, an increase in foreign direct investment (FDI) leads to an increase in migration from the southern part of the continents to the northern latitude. As a result, water availability is uncertain in rural communities and urban neighborhoods (Wong, 2004). 

Table 2. Continental scope of the water situation

Source: AQUASTAT (2010) and USCB (2010)

Faced with a continental water situation determined by financial and migratory flows, continental water sustainability would be indicated by regional public policies of the economic blocs that are based on the establishment of unit water rates determined from the contradictions between capital, extraction, availability, supply and migration. In other words, the water situational trend seems to indicate an imbalance between water availability and human needs. However, there would be enough water if it were distributed equitably across continents. Of course, this trend has a direct impact on the national water situation.

Nationwide 

The national water situation is determined by a variety of socio-environmental factors; territorial extension, hurricanes, disasters, public investment, volume of basins, aquifers, dams, level of extraction, population increase, urbanization, availability, quality, use, supply, leaks, runoff, agriculture, industrialization, thermoelectric plants, deficit, pollution, treatment and exclusion (see Table 3). 

Based on the diagnoses of the National Water Commission (CONAGUA), the National Institute of Geography and Informatics (INEGI) and the National Population Commission (CONAPO), a consequence of migration from the south to the center and north of the country stands out, which is exclusion. Due to the centrality of the federation, agriculture is concentrated in the centre of the country, but it is industry and commerce that demand a greater volume of water to provide work for a high percentage of the economically active population. However, per capita availability in the center of the country is very low compared to the south, where the amount of water per person is very high, but whose productive function is lower in activity and wages than workers in the north who suffer from severe water scarcity (Aldama,  2004). It is also important to point out that a factor of water exclusion in the north of the country is the high percentage of communities located at an altitude above 2000 meters where the cost of energy for pumping would exceed the unit price of water (Toledo, 2002).

Table 3. National level of the water situation

Fuente: BANXICO (2000), CONAGUA (2010), CONAPO (2005) and INEGI (2000)

Thus, the water situation of the center of the country would determine the national water sustainability since it is the federal power that administers the national finances. In this sense, investment seems to emerge as a determining factor of the causes and consequences exposed. In other words, an increase in the equitable demand for water would imply an increase in the cost of supply. National water sustainability would be indicated by public policies based on the establishment of the unit price of water based on its environmental conditions and economic trends aimed at equitable distribution among the residents of the south, center and north of the country. However, at the state level, other factors seem to adjust the concept of water sustainability to water rights and culture. 

Statewide

At the state level, the water situation is determined by the volume of droughts, population, density, infrastructure, extraction, supply, leakage, availability, utilization, consumption, recharge, collection, deficit, and inequity (see table 4). 

In this sense, it is cities and their industrial, commercial and consumerist dynamics that monopolize the supply of rural communities and peripheral neighborhoods (Santos, 2004). In fact, cities with more than 500,000 inhabitants have a very high demand for consumption and consequent supply of services compared to the residents of rural communities where the aquifers that supply cities, their industries and trade centers are located (Breña, 2007). This inequity is aggravated if we consider that the most excluded communities live at an altitude above 2000 meters. 

Table 4. State-level water situation

This essay has described eight areas, situations and trends of water availability, supply and consumption around which it is possible to infer public policies that are meagre in their relevance to address the water problems of scarcity, intermittent supply and unhealthiness related to the drinking water system. In this sense, the establishment of a public agenda alluding to the equitable distribution of supply and collection of drinking water service would include the variables exposed to determine a system of quotas, sanctions or subsidies to citizens. 

However, the trend of water situations in each of the areas described seems to indicate that water supply obeys a clientelistic socio-political system in which the scarcity or intermittent supply of water is an indicator of the inefficiency of public policies related to water problems. 

The description of the situational areas and the trends of supply and consumption are evidence of the complexity of water problems. It is an asymmetrical relationship between the State and citizens in which the distribution of resources is a factor that inhibits sustainable development. In other words, the percentage of leaks identified in the public network is similar to the percentage of leaks estimated at the residential level: 40 percent of water is lost due to leaks from the main network and 40 percent of water is filtered into the toilet.

Both problems could be explained from human cognition, but the social sciences have focused on the analysis of power relations between users and authorities. Explaining the waste of water in a context of scarcity from the pragmatic relations between residents and public service managers, attributing the problems to the corruption of the Mexican political system, the minimum investment in the public supply network or in the nature of supply and demand, can be complemented with the analysis of the rules.  values, perceptions, beliefs, attitudes, knowledge, competencies, intentions and personal behaviours.