ENTROPIC MANAGEMENT OF WATER IN DECENTRALISED COUNTRIES
Carlos DÃaz-Delgado1, Danilo AntÃ³n2, MarÃa Vicenta Esteller 1, Juan Antonio GarcÃa1,
Khalidou M. BÃ¢ 1, Emmanuelle Quentin1
This work presents some insight into the way in which federate countries today, especially
developing federate countries, carry out their so-called water management. Reference is also
made to one of the concepts that has had the greatest impact over the last decades due to the
degree of progress and evolution reached, which is the concept of Integrated Water Resources
Management (IWRM). Based on the arguments that support this water management process
and acknowledging water and energy resources as critical variables for sustainable
development, a methodology is proposed with physical and natural foundations for decisionmaking.
This process consists in using concepts of the environmental economy and above all
in optimising the necessary energy to satisfy the water needs for the different uses in a river
basin. Finally, it is necessary to underline that this methodological proposal is still in a
development and refinement phase within the Inter-American Centre for Water Resources
(CIRA-UAEM-Mexico) but whose partial results confer upon it a promising future as well as
a rapid evolution and implementation.
Key words: Integrated Management, River Basins, Entropy, Water Quality, Water Value,
1 1 Professor â€“ researcher, 2 Guest professor, Inter-American Centre for Water Resources,
Autonomous University of the State of Mexico (CIRA-UAEM, MÃ©xico), Cerro de Coatepec,
Ciudad Universitaria, Toluca, Mexico State, c.p. 50130.
It could be said that the International Conference on Water and the Environment in Dublin
1992, saw the rebirth of one of the most transcendental water management concepts that has
led to a reconsideration of the organisation of decision-making and management of water
resources in any country or region. This concept is called Integrated Water Resources
Management (IWRM), defined as â€œthe process of promoting the coordinated development and
management of water, land and related natural resources, in order to maximise the resultant
economic and social welfare in an equitable manner without compromising the sustainability
of the ecosystemâ€. Although it can be argued that this concept, or a very similar one, has
existed for a long time (BISWAS, 2004; RAHAMAN & VARIS, 2005, EMBID, 2003) the
important factor is not when it appeared, but that it has been improved today and is envisaged
as a feasible way to solve the indisputable water crisis faced, and above all in decentralised
It is worth mentioning that a classification has been generated, even among decentralised
countries, based on the level of existing development. Indeed, the social, economic,
educational and development situations present conditions for which the environmental
protection and organisation must be simply different. In agreement with recent studies (CAPNET
et al., 2008), the legal framework existing in federate (decentralised) countries is
considered as sufficient to support the management and protection of the natural resources of
a country. However, in practice, the applicability of this legal framework leaves a lot to be
desired. On the other hand, the level of autonomy, which the basin organisations enjoy, is
very limited in the best of the cases and generally requires the approval of national agencies,
attending to â€œpolitically acceptableâ€ reasons in detriment of a management and decisionmaking
that benefits the social-ecosystem.
Some countries, like Mexico and Brazil, have modernised their discourse and even their laws,
introducing holistic approaches for managing water resources. Unfortunately, things are very
different in reality, as the difference between the objectives, actions undertaken and the results
obtained is indisputable. These differences are apparently attributable to the lack of human,
economic and financial resources, and to the lack of sufficient technological and institutional
coordination to implement this organisation. That is why it is currently necessary to
implement participative approach strategic planning processes for integrated water resources
management based on a high action output and prioritised integration of components to be
The process required to manage natural resources and especially water, requires a change in
the organisational paradigm and above all a change in mindset of each and every one of the
members of the society in question. Today the concept of IWRM has been re-orientated
based on the framework of participative strategic planning where the changes are gradual, but
where, through the tactical planning phase, high impact results can be obtained in the shortrun
that are consistent with the strategic vision defined.
One of the generalities that arise in decentralised countries is that the water that reaches a
river that crosses more than one entity (state or department) becomes federal jurisdiction and
this water resource cannot be managed on a local level. It is precisely in this aspect where the
methodological management proposal presented here takes on singular importance as, before
the water reaches the federal river, the management will be economically more profitable.
Thus, the theory of entropic water management (DÃAZ-DELGADO et al., 2005) is presented
within the framework of proposals to implement best water management practices in
decentralised countries. This proposal aims to show a methodology which, based on real,
physical and natural facts, guides decision-making on water management, avoiding the
temptations of economic manipulation through subsidies that make any effort to optimise the
The attribution of value to natural resources is undoubtedly an arduous and difficult task.
Firstly, because it is usually measured in monetary terms, and money and nature are governed
by different laws. Money is governed by the laws of mathematics, whilst nature is governed
by the laws of physics (SOODY, 1926). Mathematics allows the quantities to increase in
agreement with the rule of composite interest, and other similar rules, whilst physics is
governed by the second law of thermodynamics, namely, entropic degradation. This
fundamental dichotomy explains the difficulty that exists to place a monetary value on natural
assets and elements.
The quantity of water that exists on the Earth remains relatively stable. In abstract terms, this
volume seems to be more than sufficient to satisfy all the human needs both at the present
time and in the near future. In fact, the quantities available are much less. Firstly, because
the natural function of water is not for the exclusive use by human societies. Water is also the
main support for the ecosystems that exist on the planet. This determines that to use water
without damaging nature, and thereby, indirectly, human societies, the socio-bio-hydrological
cycles must be taken into account. That is why the use of water is limited by the need for the
specific configuration of local, regional and global socio-ecosystems.
The main problem that human beings are experiencing with water is above all quality and to
a much lesser degree, quantity. Entropic degradation caused by human consumption
intensely affects the quality of water and to a lesser degree the volumes.
The fact is that the natural recycling produced by solar energy (evaporation, photosynthesis)
does not manage to purify all the waste water that is continuously produced.
Due to the increasing volumes of wastewater of a human origin, which are also concentrated
in relatively small areas, the natural recycling processes are insufficient to purify them.
Different types of treatment systems or plants are installed as a way to correct this situation.
The treatment processes use, either directly or indirectly, enormous quantities of fossil fuels.
It is obvious that fossil fuels are solar energy from the past, accumulated into finite volumes.
When the oil, gas and coal run out, this planet will be left with the only realistic source of
renewable energy: solar radiation.
In general, what gives value to water is, above all, its quality. Water of certain qualities (for
example toxic water) could even have a value definable as â€œnegativeâ€, as it requires large
amounts of energy to be eliminated or treated for later use, whilst other waters that do not
require any treatment may have a high value. In other words, what gives value to water is
above all the â€œquality in quantityâ€.
II. CRITERIA AND INDICES TO CHARACTERISE THE QUALITY OF WATER
Determining the quality of water refers in general to the possibility of it being used in
economic, social and environmental activities. In qualitative terms, higher quality water is
water that has a low salt or dissolved gas content, which does not contain pathogenic microorganisms,
with very low levels of organic matter and with few or no particles in suspension.
In general, water with these characteristics is appropriate for human consumption. There are
several water quality coefficients, generally calculated based on the determination of the
concentrations of salts and different types of contaminants contained therein. The National
Water Commission (CONAGUA, Mexico) has used a coefficient that varies from 0 to 100,
where 0 is the worst quality. Quality is calculated through the following equation:
i I iWi
Where: I: General quality coefficient; Ii: Quality coefficient of the considered parameter; Wi:
Weighting of the parameter considered. The weighting awarded to the parameters is shown
on Table 1.
Water quality is also characterised in agreement with official government regulations that
establish maximum admissible limits of contaminants in water for different uses (human
consumption, irrigation, discharges into natural water, etc).
Industrial wastewater is also defined in agreement with the different contaminants it contains.
Several coefficients have been established to define the degree of contamination; one of them
is the chimiotox, or toxic weighting factor (Ftox) which was established by the Plan dâ€™action
St Laurent de Quebec, Canada. The equation to calculate it is (DENIZEAU & RICARD,
1998): ( )
( ) l
Where: Ftox i : the toxic weighting factor of parameter i; 1 mg/l: an arbitrary reference; CPSi :
the most sensitive water quality criterion of parameter i.
Based on the preceding equation the chimiotox unit or UCi is calculated: UCi = Chargei x
Ftox i. Then the chimiotox units of each contaminant are added up to define the chimiotox
coefficient (IC) and thus know the contaminant charge of an effluent, and therefore, the
relative water quality.
Another way of facing up to the problem is via the definition of environmental indicators that
indirectly provide the required information. The indicators are variables or values derived
from variables that provide information about a phenomenon (BARRIOS ORDOÃ‘EZ and
GONZÃLEZ MORA, 1999).
The variables used by the aforementioned authors are BOD5 (biochemical oxygen demand),
(ammoniac nitrogen), DO (dissolved oxygen) and FC (faecal coliforms). This
approach facilitates the analysis, although really it only provides elements about the effect of
water degradation processes without giving a complete idea of the energy and entropic cycles
that take place in water systems.
III. JUSTIFICATION OF AN INSTRUMENT FOR AN ENTROPY ANALYSIS OF
When the time comes to make decisions on water issues, the decision-makers must face up to
a wide range of real data and elements, which include geographical, geological, ecological,
hydrological, social-cultural and technological aspects, as well as water quality coefficients or
indicators, which are not always easy to interpret.
With respect to water, as in other similar fields, the final decisions are usually political ones,
and in the majority of the cases, their defining element is an economic one.
However, in economic analyses that lead to the adoption of public water policies, the
assessment of the â€œvalueâ€ of the resource only takes aspects related to the monetary value into
account. To make this situation worse, water is often considered as an inexhaustible resource
and that it suffices to construct sufficient capital assets, such as dams or lines of wells, to
obtain it. In fact, the loss of value resulting from its use is unknown as is the cost required to
return a value to it that will permit its re-utilisation. If a â€œnaturalâ€ value can be assigned to
water, expressed in one single coefficient that shows the degree of entropic degradation, it
will be easier to perform an analysis and make a decision on firm and sure bases.
IV. WATER MANAGEMENT THEORY: ENTROPIC MANAGEMENT
1. THE CONCEPT OF ENTROPY
Entropy is a complex concept that aims to describe the natural direction of physical processes
in the universe. These tend to occur in an organised and disorganised fashion as well as
heterogeneously and homogeneously. The energy concentrated somewhere in space tends to
diffuse in all directions. This diffusion can locally be hindered by other physical forces, such
as gravitational attraction. These barriers to the global dissemination of energy produce
almost closed systems that form circumscribed areas where the law of entropy acts. If the
celestial bodies were not to emit or receive energy (or its concentrated version: matter) they
could be considered as closed systems and for these cases the Second Law of
Thermodynamics could be applied, whose formulation sustains: “The entropy of a closed
system never decreases and whenever possible it increasesâ€. Really, the only entirely
closed system is the entire universe, and this is where the aforementioned concept is applied.
The concept of entropy is also applied to open (or half-open) systems. Likewise, these tend to
become disorganised and unify their matter and energy levels. Due to their open character,
they may experience local entropy reduction processes that are explained by an increase in
entropy elsewhere. The general balance is an increase of entropy. The geological evolution
of the Earth is the result of the interference of two entropic tendencies, that of the Sun, which
in its maturity diffuses and therefore â€œsharesâ€ its energy, and that of the Earth itself, which,
similarly, although in a less intense manner, is continually and sometimes obliviously
radiating its energy flow. From the practical viewpoint, entropy is expressed in a series of
physical phenomena which, given the appropriate conditions, take place in one single
2. THE ENTROPIC VALUE OF WATER
The volume of water on the planet is finite but its theoretic potential for use is unlimited.
What is really measured is the speed of flow. This depends mainly on energy and the energy
available on the Earthâ€™s surface is limited, almost entirely supplied by solar radiation.
Another long-term limiting factor is the final irreversibility of its entropic degradation, which,
although expressed above all at very large time scales, may be accelerated via human
Environmental contamination can be perceived as the result of the material and heat discharge
in the environment (water, air and/or soil) due to antropic production or consumption
activities. When a compound is added to water, the component dissolves and mixes in the
medium. This dissolution and mixture implies an increase in the entropy of the solution and
an increase in the degree of contamination, which suggests that an increase in entropy implies
water contamination. Water contamination can, then, be seen as a process where water that
initially has low entropy, eventually returns to the medium with higher entropy due to the
antropic use that is given to it and therefore the entropy of the environment that receives it
increases. (SING, 2000).
The entropic value of water is really its value assessed in the framework of the entropic
evolution of life on the planet. It is a value that decreases as the entropy increases and which
therefore could be called more correctly: â€œanti-entropicâ€ value. As human beings consider
that entropy is in fact a devaluation of the resources, the expression, entropic value, will be
used to define the absence of devaluation, or in other words, the absence of entropy.
The entropic value of water is related to the consumed / used energy to take the liquid to a
state of lesser entropy that is sought to be established. In that regard, the entropic value
comes from the energy required to obtain a specific quality of water based on a reference
In natural systems, the greater entropic value is achieved from the condensation of the water
vapour of the atmosphere in the clouds and its precipitation by way of rain, snow or hailstone.
The falling of water as well as its subsequent run-off towards lower potential energy levels,
implies an increase in entropy and therefore a loss of the entropic value of the resource.
Following the precipitation, the rainwater runs off and/or infiltrates. Substances are dissolved
and incorporated into its flow giving rise to additional losses of its entropic value. As it
flows, the water is transformed into a more and more suitable medium for the development of
live organisms. The physiological photosynthetic functions may locally produce an entropic
valuation of the resource, whilst the remaining metabolic functions tend to reduce the value.
The accumulated effect of these processes leads to an increase in the entropy of the water.
On the other hand, the human use of water is a factor that accelerates the increasing
deterioration of its value, which is added to the degradation due to natural processes.
Irrigated farming, which uses a lot of water when considered in terms of volume, uses water
of a certain quality and returns it to the natural medium with a lower quality. The value loss
due to agriculture depends on the irrigation practices and systems used. In some cases, high
quality water (greater entropic value) is used and when discharged it is highly contaminated
with agrochemicals or salts (less entropic value). In that case, the value loss is very great.
Cities, on the other hand, despite consuming less water than agriculture, tend to be great water
degrading factors. The majority take water from nature, submit it to certain potabilisation
treatments (that consume energy), raising its entropic value and then return it to the medium
charged with numerous contaminants. The re-utilisation of urban wastewater, which means
raising the entropic value again, requires larges quantities of energy, which are often out of
reach of the societies in question.
Industrial activities, on the other hand, generally but not always have intensive harmful effects
on water resources. The water degradation potential by the industrial activity is very great.
Different methodologies have been applied in practice to calculate the value of water quality.
Although a method based on the entropic value cannot be easily expressed in quantitative
terms, it is an instrument that can be used to define, though qualitatively, the value scales
required to formulate appropriate strategies to optimise the use of available water resources.
V. THE ENERGY CYCLE OF WATER
One way of presenting the water cycle is via the energy exchanges that take place in the
different processes whereby water changes state, physical or chemical properties, or its
position in space. The majority of the energy consumed in the water cycle comes (directly or
indirectly) from solar radiation. However, there is a smaller proportion that comes from
geothermal sources, giving rise to the heating of groundwater, and of certain hydrothermal
springs. A list of energy-hydrological cycle phenomena and processes are shown in Table 2
and Figure 1.
1. NATURAL RECYCLING SYSTEMS
All the wastewater that is not artificially recycled is integrated into the hydrological cycle and
subjected to natural recycling systems. The planetâ€™s capacity to naturally recycle water is
limited, both locally and globally. On a local level, water is usually left for a certain period of
time with deteriorated quality conditions, until discharged to the sea or evaporated. In both
cases it is reintegrated into the natural system in the form of rain, snow or hailstone.
On a global level, untreated wastewater tends to be dissolved in oceans, seas and lakes, being
incorporated into them and reducing their quality. This process is clearly visible near the
coasts where the characteristics of sea water are considerably deteriorated due to the
contributions of cities and industries. Seawater is surface water with high entropy (and
therefore with a low entropic value). This natural value, which has already been reduced, is
decreased even more by human action.
WATER CLASSIFICATION CRITERIA
A series of criteria have been used to classify water according to its entropic value. These are
in turn associated with entropic type processes and with the necessary energy requirements to
take the water from the lower levels (with less entropic value) to other higher levels. In some
cases, when the processes are irreversible, this â€œelevationâ€ in entropic level may not be
The following major criteria are used:
The entropic value tends to drop as the water descends, releasing potential energy. The
water from the clouds and mountains is more valuable than the water from the rivers, sea
or plain aquifers;
The entropic value also decreases when the concentration of dissolved substances
The entropic value decreases when the heterotrophic (non photosynthetic) organisms
increase. Photosynthetic organisms have the opposite effect during the time the
photosynthetic function takes place. The entropic value also decreases when the organic
matter concentration increases. After a certain threshold, the increase in entropy
(consequently decrease of its entropic value), may lead to the reduction and even
disappearance of the vital processes and organic matter;
The entropic value decreases as the water contamination increases (toxicity for different
forms of life).
There are several reasons for a reduction in the quality of water. Some are natural and
others are derived from the type of use. Therefore, there can be water with very different
characteristics that is classified at the same level. The reason is that all types of water
require comparable quantities of energy to be taken to the levels of reference.
Table 3 shows the different types of waters classified in agreement with their level (value), as
well as the possible use, geological position and presence of life.
AWARDING THE ENTROPIC VALUE
To calculate the entropic value a mixed, qualitative â€“ quantitative, method is proposed.
Firstly the entropic values are awarded to the waters in agreement with the aforementioned
criteria, granting 10 to the maximum entropic value (water from high, newly condensed
clouds) and 0 to non-contaminated seawater with medium salinity. The intermediate values
are assigned by combining different quantitative and qualitative criteria. Negative values are
awarded to hypersaline or highly contaminated waters. The following equation is proposed to
calculate the entropic value:
Where: VE: is entropic value; NE: is entropic level (defined qualitatively) and Mc: are the
megacalories required to evaporate 1 m3 of water at a temperature of 15Âº C and at water level
pressure. In agreement with the above equation, the different entropic levels would
correspond to the values presented in table 4.
PARAMETERS TO DEFINE THE ENTROPIC VALUE LEVELS
The decrease in entropic value is a natural phenomenon that occurs from the moment that
water vapour condenses forming clouds, and especially when it falls to the ground in the form
of rain. At that time the waters begin to flow, losing potential value, salinity increases and it
is charged with organisms and organic matter. The process is usually reverted locally and
temporarily, for example, due to the photosynthetic action of algae or other plants, due to
water filtration in certain appropriate geological formations, or to the interaction of the latter
or other factors. This occurs in those cases where salinity is too high, or any other physicalchemical
condition such as the pH or the temperature, which are, in general, limiting
conditions for life. The general tendency of earth landscapes, in normal conditions, is towards
an increase in salinity and organic matter content.
Thus, entropic quality can be measured via a mixed scale based on total dissolved solids
(TDS) and/or on the biochemical demand of oxygen (BDO).
Normally, the antropic use of water produces an acceleration of these processes and therefore
it is possible to use the same method to assess the quality of liquid waste.
The majority of domestic wastewater is charged with organic matter and decomposing
organisms (e.g. bacteria and protozooaria) and it normally has higher total dissolved solid
rates than the original water. In those cases, the levels of TDS and BDO are to a great extent
the reason for the change in quality.
The admissible BDO levels (in mg/l) in agreement with Official Mexican Standards, for water
discharged into natural waterbodies must be less than 150 in river water used for irrigation, 75
in water for urban use, 30 in rivers used for aquatic life protection, 75 in coastal waters used
for leisure and zero in drinking water (NOM, 1996).
However, certain wastewaters, above all from industry, have a toxicity that may prevent the
life of organisms. In those cases, the BDO is not an appropriate measure to determine nonbiodegradable
organic matter and may be replaced by Chemical Demand of Oxygen (CDO).
Other processes to reduce the entropic value are added in certain situations, which are difficult
to quantify via BDO and CDO. These are cases where the presence of metals and other
potentially toxic contaminants are in suspension or in solution in the water.
In those cases, it may be necessary to add an additional compound parameter (metals and
other contaminants: MOC) including metal concentrations (e.g. Zn, Cu, Pb, Hg, Cd, Cr, Ni,
Fe and Al) and other toxic substances (arsenic, cyanide, phenols, etc.). The concentrations
corresponding to each one of the entropic levels are presented in Tables 5, 6, 7 and 8.
Table 5 presents the maximum permissible concentrations of metals and other contaminants
for the water to be able to be discharged into the urban or municipal sewage systems in
agreement with Mexican standards (NOM, 1996). Table 6 shows the maximum permissible
concentrations for water to be able to be discharged into natural waterbodies and Table 7
includes the maximum permissible concentrations for drinking water. The approximate levels
of TDS, BDO, CDO and MOC proposed for each type of entropic quality of water are
presented in Table 8.
The potential energy conditions, related to the gravitational position of the water considered
must be added to this. This position is expressed in height in metres above the local base
level of the basin. This energy can be positive in the case of surface water and shallower
groundwater, or negative in deeper groundwater.
As the entropic value of water drops it becomes more onerous, from the viewpoint of the
energy required, to return it to optimal conditions of use. Saltwater can be desalinised either
naturally or artificially and energy is required in both cases. Water with a higher BDO or
CDO can be treated as a result of natural processes (based on solar energy) or treated
artificially in appropriate plants, whose operation also requires energy. The biological or
chemical treatment of water that contains metals or other similar toxic substances, on the
other hand, may give rise to toxic accumulations in the biota, in the soils and / or in
sediments. This water can be treated and, consequently, the metal or toxic substance
concentration can be reduced. Anyway, the processes required to achieve a significant
decontamination usually entail an astronomical energy cost.
Finally, as a result of the gravitational flow (potential energy loss) water also becomes more
â€œexpensiveâ€ in energy terms, as to be used the water must be â€œelevatedâ€ physically to the
consumption places with the subsequent increase in cost.
APPROXIMATE RELATIONSHIP BETWEEN THE ENTROPIC VALUE, THE BDO
AND THE CDO
An attempt has been made to establish a relationship between the Entropic Level, the Entropic
Value calculated via the aforementioned equation, and the BDO and CDO that are observed in
natural and / or waste water. This relationship is approximate, but it permits presenting the
different levels and values in quantitative terms. The equivalences proposed between these
levels and parameters are presented in Table 9.
The energy cost required to raise the water quality from one level to another varies depending
on the type of entropic degradation that the water has undergone and on the technology used.
In natural environments, recycling takes place naturally and the energy expenditure is the
radiant solar energy required to evapotranspire or oxygenate the degraded water, taking it to
the necessary level of reference. In artificial systems, the recycling or potabilisation takes
place by treating water, using different methods and energy sources. The energy expenditure
to evaporate water from natural waterbodies at an ambient temperature of 20Â° C is 600,000
kcal per m3.
THE COST OF ARTIFICIAL RECYCLING
Degraded or salinated water (with low entropic level) can be recycled or potabilised via
artificial procedures. Different technologies can be used, the most economic methods being
biological methods (e.g. stabilisation lagoons), which are generally appropriate for small
flows (small and medium towns). More complex treatment plants with both biological and
physical-chemical processes are normally used for larger flows, from large urban and
industrial areas. These processes include recycling, elimination and / or incineration of waste
sludge. In both cases (biological and physical-chemical methods), the product obtained do
not have drinking quality. To achieve this, even more sophisticated methods that use more
energy are required.
The difference between these methods is the cost. Biological methods are more economical
and, in general, require minimal operation expenses. These variables depend on the
geographical conditions of the place, but are normally less than US$ 0.01 per m3.
The physical-chemical methods (industrial origin water) require considerable investments or
around 1 to 2 billion dollars for a waste water flow of 5 to 10 m3 per second. The operating
expenses vary according to the conditions of each case but on average they are estimated at
US$ 0.03 per m3 of treated water. If the capital depreciation cost is added, the cost would be
somewhat higher, around US$ 0.05 per m3 (CUM, 1999; TRIPOWER SYSTEMS, 1997,
SATO et al., 2007).
Evaporative systems are even more costly. The desalination of 1 m3 of seawater costs around
US$ 3 per cubic metre using solar energy, whilst using fossil fuels or electricity, the cost
would be several times greater (US$ 10 to 50 per m3 depending on the cost of oil or electricity
in each place and not considering State subsidies in the energy cost).
In terms of entropic levels, treated industrial and urban water does not exceed the entropic
level of 4 or 5, whilst evaporated/distilled water reaches a level of 8 or 9. This shows the
limitations of technology, which is still very strongly dependent on the natural cycle.
Thus, costs increase logarithmically as the entropic level rises. With the available technology,
taking water from level 1 or 2 to level 4 costs approximately US$ 0.03-0.05 per m3, whilst
taking it to level 8 costs 100 to 300 times more (US$ 3 to 10 ).
Table 10 shows how, as an approximate general rule, the value in US$ is doubled or trebled
for each level, in other words, it decreases two or three times in value when it drops one level.
The monetary cost really depends on the technology and the amounts of wastewater
produced/treated in a given place.
New and more appropriate technologies could, undoubtedly, reduce that difference to 1.5 or
1.8 between the levels.
The above depends on several elements that can substantially modify the results, the most
important element being technology. The technological cost geometrically increases every
time an attempt is made to raise the water quality one more level. A technological coefficient
must thus be applied to give the entropic value meaning and an illustrative dimension.
The proposal is then to multiply the entropic value Ve by a technological coefficient of value
1 for water with entropic value 0 (sea water), doubling this for each successive increase in
level. This doubling aims to respond to the increasing technological difficulties involved in
the attempt to increase the quality of water. In the last change (from level 9 to level 10;
equivalent the entropic values of 0.99 and 1.00 respectively), the technological coefficient
calculated is equal to 512. Thus the corrected value Vc is obtained by multiplying the
entropic value by the technological value. Table 11 shows the technological coefficients
usable for each level, and the corrected value in agreement with the following equation:
Vc = Ve(Ct )
Where, Vc : is the corrected value; Ve : is the entropic value; and Ct : is the technological
There is no doubt about the complexity of the water problem in the majority of developing
countries, or about the increasing scarcity of available fossil energy, and these aspects have
become critical development variables for these people. Indeed, in these decentralised
countries, some of which are characterised by the scarcity of water resources and others by
the excess or high degradation of the resource, in all the cases there is an imminent need to
coordinate and organise on an intersectoral, social, scientific and political level to be able to
improve the decision-making. The only way to solve water problems is within a scenario of
consensus and rationality, and sustainability will only be possible by creating and / or
strengthening local capacities with a regional approach based on the management and
appropriation of knowledge.,
It is finally necessary to point out that it is not a question of modifying the existing sectoral
structure, or of dividing the powers and responsibilities, and much less of the disappearance
of the institutions, but rather giving them the meaning for which they were designed and
constituted, combining efforts, coordinating plans, programmes, projects and actions to
maximise the benefits and social and environmental welfare with the least possible
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Table 1. Weighting of the water quality parameters
Parameter Weighting Parameter Weighting Parameter Weighting
4. Fats and oils
9. Total hardness
10. Nitrate N
11. Ammoniac N
Table 2. List of phenomena and processes from the energy â€“ hydrologic cycle
Phenomena and processes Energy behaviour associated with the
phenomenon / process
Condensation of atmospheric water
Precipitations Releases potential energy, kinetics P
Evaporation during fall Absorption of energy Ep
Impact of precipitation Release of energy I
Evaporation associated with plant
Infiltration Releases potential energy In
Runoff Releases potential energy, kinetics es
Erosion and transport of materials in
Releases potential energy, kinetics et
Dissolution and transport of
Absorption and release of chemical
energy, release of potential energy
Direct evaporation of continental
Transpiration (biological) Absorption T
Photosynthesis (development of
Metabolism of autotrophic
Release of chemical / thermal energy
Decomposition and metabolism of
Release of chemical / thermal energy
Oceanic evaporation Absorption Eo
Convective ascent Absorption Ac
Geothermal heating Absorption Cgt
Hydrothermal and volcanic ascent Absorption Ahv
Table 3. Entropic level of water
Presence of life
High, atmospheric Very few organisms,
Low, atmospheric Few organisms, few
Organisms of low to
high hills, , plateaux
Very acid rain Hilly areas, low
Plains, low hills,
intermediate to very
organisms in rivers and
lakes, locally excess of
nutrients. Discharges of
irrigation water may
Low, arid areas,
subsoil of variable
organisms in brackish
lakes. Discharges of
irrigation water may
Spa water Intermediate
Sea level, depressed
subsoil of variable
organisms in seas and
lakes, few in urban
0 a – 5
Brine Ground brine
Ground brine water Few organisms due to
toxicity, possible local
< -5 Saline Salt deposits Industrial salt production High toxicity industrial discharges Salt deposit Absence of organisms Table 4. Relative entropic value for each entropic level Entropic level Relative entropic value 10 1.00 9 0.99 8 0.96 7 0.91 6 0.84 5 0.75 4 0.64 3 0.51 2 0.36 1 0.19 0 0 0 a â€“5 -0.21 a -2.25 < -5 < -2.25 Table 5. Permissible limits of metals and other contaminants in waste water discharges to urban or municipal sewage systems (MOC, daily mean, in μg/l) Metals Maximum permitted value (μg/l) Zinc 9.0 Copper 15.0 Cadmium 0.75 Hexavalent chrome 0.75 Lead 1.5 Total nickel 6 Mercury 0.015 Other contaminants Total arsenic 0.75 Total cyanide 1.5 Fats and oils 75 Source: Official Mexican Standard NOM-002-ECOL-1996 Table 6. Permissible limits of metals and other contaminants in treated waste water discharged into rivers, to protect aquatic life (MOC, daily mean, in μg/l) Metals Maximum permitted value (μg/l) Zinc 20 Copper 6 Cadmium 0.2 Total chrome 1 Lead 0.4 Total nickel 4 Mercury 0.01 Other contaminants Total arsenic 0.2 Total cyanide 2 Source: Official Mexican Standard NOM-001-ECOL-1996 Table 7. Permissible limits of metals and other contaminants for drinking water (MOC, daily mean, in μg/l) Metal Maximum permitted value (μg/l) Zinc 5.0 Copper 2.0 Iron 0.3 Aluminium 0.2 Manganese 0.15 Total chrome 0.05 Lead 0.025 Mercury 0.001 Other contaminants Arsenic 0.05 Cyanide (CN-) 0.07 Nitrates (as N) 10.0 Nitrites (as N) 0.05 Phenols or phenol compounds 0.001 Source: Official Mexican Standard NOM-127-SSA1-1994 Table 8. Entropic level of water measured based on BDO, CDO, STD and MOC. Natural surface water Waste or contaminated water Entropic level Type of surface water BDO5 Type of wastewater BDO5 * CDO * MOC Metal and other contaminants Groundwater Salinity STD, ppm 10 High, newly condensed clouds 0 0-10 9 0 10-40 8 Low clouds, rain, snow 0 40-80 7 Springs, mountain torrents <10 mg/l Below limited established in level 7 80-150 6 High river courses, mountain lakes 10-20 mg/l Moderately acid rain 0 Maximum limits for drinking water (See Table 5) subsurface flows, fresh water springs 150-300 5 Intermediate river courses, intermediate lakes, effluents of certain wetlands 20-30 mg/l Very acid rain 0 Intermediate concentrations between levels 2 and 6 Fresh, quite shallow groundwater 300-600 4 30-45 mg/l 3 Low river courses, plain lakes, oxygenated wetlands 45-60 mg/l Irrigation drainage, treated wastewater 0-60 mg/l 0-120 mg/l Intermediate concentration between levels 4 and 7 Quite shallow, slightly brackish groundwater; fresh deep groundwater 600-1000 2 Eutrophicated lakes and wetlands, Slightly brackish lakes 60-80 mg/l Irrigation drainages, partially treated wastewater 60-80 mg/l 120- 160 mg/l Maximum limits for discharges into rivers (See Table 6) Slightly brackish, deep groundwater; quite shallow, brackish water 1000- 2500 1 2500- 5000 0 Brackish lakes and seas <60 mg/l Intermediate urban and industrial discharges 80-200 mg/l 160- 400 mg/l Intermediate concentration between levels 2 and y 4 Salted groundwater 5000- 35000 0 a â€“5 Brine 0 Highly contaminated urban and industrial discharge >200
discharge limits, See
< -5 Saline 0 High toxicity industrial discharges Above limit established in level 2 Salt deposits >300000
* for merely estimation purposes it has been established that BDO/ CDO = 0.5
Table 9. Relationship between Entropic value, BDO5 and CDO.
Entropic level Entropic value BDO5
7 0.91 < 10 mg/l 6 0.84 10-20 mg/l 5 0.75 20-30 mg/l 4 0.64 30-45 mg/l Levels 4 to 10 do not correspond to wastewater Levels 4 to 10 do not correspond to wastewater 3 0.51 45-60 mg/l 0-60 mg/l 0-120 mg/l 2 0.36 60-70 60-70 mg/l 120-140 mg/l 1 0.19 70-80 70-80 mg/l 140-160 mg/l 0 0 80-200 mg/l 160-400 mg/l 0 a â€“5 -0.21 a â€“2.25 < 80 mg/l > 200 mg/l > 400 mg/l
< -5 < â€“2.25 Tends to 0 Tends to 0 Table 10. Approximate cost to raise the entropic value of water To raise from the relative level to level 8 (potable) (several methods) Biochemical methods to raise from relative level to level 5 (for irrigation) Biological methods to raise from relative level to level 5 (for irrigation) Entropic level Entropic value Approximate cost per m3 in US$ Approximate cost per m3 in US$ Approximate cost per m3 in US$ 10 1.00 9 0.99 8 0.96 7 0.91 < 0.05 6 0.84 0.05-0.3 5 0.75 0.1 to 0.5 4 0.64 0.2 to 1 0.01-0.10 3 0.51 0.4 to 3 0.02-0.15 2 0.36 1 to 10 0.03-0.20 0.005- 0.10 1 0.19 0.05-0.20 0.01- 0.20 0 0 3 to 30 0.10 to 0.5 0 to â€“5 -0.21 to â€“ 2.25 > 30 0.5 to 10
< -5 < â€“2.25 > (0.5 to 10)
Table 11. Entropic value corrected by technological advance
Entropic level Entropic value Technological
(due to technological coefficient)
10 1.00 1024 1024
9 0.99 512 507
8 0.96 256 246
7 0.91 128 116
6 0.84 64 54
5 0.75 32 24
4 0.64 16 10
3 0.51 8 4
2 0.36 4 1.4
1 0.19 2 0.38
0 0 1 0
0 a â€“5 -0.21 to â€“2.25 2 to 32 – 0.42 to – 72
< â€“5 < â€“2.25 > 32 > -72
Figure 1. Energy â€“ hydrologic cycle diagram