An accurate model for RO process has significant importance in the simulation and optimization proposes. A steady state model of RO process is developed based on solution diffusion theory to describe the permeation through membrane and thin film approach is used to describe the concentration polarization. The model is validated against the operation data reported in the literature. For the sake of clear understanding of the interaction of feed temperature and salinity on the design and operation of RO based desalination systems, simultaneous optimization of design and operation of RO network is investigated based on two-stage RO superstructure via MINLP approach. Different cases with several feed concentrations and seasonal variation of seawater temperature are presented. Also, the possibility of flexible scheduling in terms of the number of membrane modules required in operation in high and low temperature seasons is investigated A simultaneous modelling and optimization method for RO system including boron removal is then presented. A superstructure of the RO network is developed based on double pass RO network (two-stage seawater pass and one-stage brackish water pass). The MINLP problem based on the superstructure is used to find out an optimal RO network which will minimize the total annualized cost while fulfilling a given boron content limit. The effect of pH on boron rejection is investigated at deferent seawater temperatures. The optimal operation policy of RO system is then studied in this work considering variations in freshwater demand and with changing seawater temperature throughout the day. A storage tank is added to the RO layout to provide additional operational flexibility and to ensure the availability of freshwater at all times. Two optimization problems are solved incorporating two seawater temperature profiles, representing summer and winter seasons. The possibility of flexible scheduling of cleaning and maintenance of membrane modules is investigated. Then, the optimal design and operation of RO process is studied in the presence of membrane fouling and including several operational variations such as variable seawater temperature. The cleaning schedule of single stage RO process is formulated as MINLP problem using spiral wound modules. NNs based correlation has been developed based on the actual fouling data which can be used for estimating the permeability decline factors. The correlation based on actual data to predict the annual seawater temperature profile is also incorporated in the model. The proposed optimization procedure identified simultaneously the optimal maintenance schedule of RO network including its design parameters and operating policy. The steady state model of RO process is used to study the sensitivity of different operating and design parameters on the plant performance. A non-linear optimization problem is formulated to minimize specific energy consumption at fixed product flow rate and quality while optimizing the design and operating parameters. Then the MINLP formulation is used to find the optimal designs of RO layout for brackish water desalination. A variable fouling profile along the membrane stages is introduced to see how the network design and operation of the RO system are to be adjusted Finally, a preliminary control strategy for RO process is developed based on PID control algorithm and a first order transfer function (presented in the Appendix). / Government grant

Desalination technology provides fresh water to the arid regions around the world. Multi-Stage Flash (MSF) distillation process has been used for many years and is now the largest sector in the desalination industry. Top Brine Temperature (TBT) (boiling point temperature of the feed seawater in the first stage of the process) is one of the many important parameters that affect optimal design and operation of MSF processes. For a given pressure, TBT is a function of Boiling Point Temperature (BPT) at zero salinity and Temperature Elevation (TE) due to salinity. Modelling plays an important role in simulation, optimisation and control of MSF processes and within the model, calculation of TE is therefore important for each stages (including the first stage, which determines the TBT). Firstly, in this work, several Neural Network (NN) based correlations for predicting TE are developed. It is found that the NN based correlations can predict the experimental TE very closely. Also predictions of TE by the NN based correlations were found to be good when compared to those obtained using the existing correlations from the literature. Secondly, a hybrid steady state MSF process model is developed using gPROMS modelling tool embedding the NN based correlation. gPROMS provides an easy and flexible platform to build a process flowsheet graphically. Here a Master Model connecting (automatically) the individual unit model (brine heater, stages, etc.) equations is developed which is used repeatedly during simulation and optimisation. The model is validated against published results. Seawater is the main source raw material for MSF processes and is subject to seasonal temperature variation. With fixed design the model is then used to study the effect of a number of parameters (e.g. seawater and steam temperature) on the freshwater production rate. It is observed that, the variation in the parameters affect the rate of production of fresh water. How the design and operation are to be adjusted to maintain a fixed demand of fresh water through out the year (with changing seawater temperature) is also investigated via repetitive simulation. Thirdly, with clear understanding of the interaction of design and operating parameters, simultaneous optimisation of design and operating parameters of MSF process is considered via the application MINLP technique within gPROMS. Two types of optimisation problems are considered: (a) For a fixed fresh water demand throughout the year, the external heat input (a measure of operating cost) to the process is minimised; (b) For different fresh water demand throughout the year and with seasonal variation of seawater temperature, the total annualised cost of desalination is minimised. It is found that seasonal variation in seawater temperature results in significant variation in design and some of the operating parameters but with minimum variation in process temperatures. The results also reveal the possibility of designing stand-alone flash stages which would offer flexible scheduling in terms of the connection of various units (to build up the process) and efficient maintenance of the units throughout the year as the weather condition changes. In addition, operation at low temperatures throughout the year will reduce design and operating costs in terms of low temperature materials of construction and reduced amount of anti-scaling and anti-corrosion agents. Finally, an attempt was made to develop a hybrid dynamic MSF process model incorporating NN based correlation for TE. The model was validated at steady state condition using the data from the literature. Dynamic simulation with step changes in seawater and steam temperature was carried out to match the predictions by the steady state model. Dynamic optimisation problem is then formulated for the MSF process, subjected to seawater temperature change (up and down) over a period of six hours, to maximise a performance ratio by optimising the brine heater steam temperature while maintaining a fixed water demand.

Thesis (MScEng (Civil Engineering))- -University of Stellenbosch, 2011 / ENGLISH ABSTRACT: The limited water supply and an increasing water demand means that the effective management of water resources becomes much more important than in the past. The implementation of water demand management / water conservation (WDM/WC) projects are usually used as a crisis management tool to reduce immediate water shortage and to allow time for the planning and construction of infrastructure to increase water supply. It is however possible to incorporate WDM/WC into integrated water resource management and to use WDM/WC as an economic viable option for the upgrade of infrastructure to balance supply and demand. Existing economic evaluation methods to compare different options with each other were used to evaluate WDM/WC measures. Literature showed that to perform an economic evaluation of WDM/WC measures, the costs associated with the implementation of the WDM/WC measures, as well as the expected water saving from the implementation of the WDM/WC measure, must be known. Models were developed to estimate the expected water savings from different WDM/WC measures. The economic impacts of specific WDM/WC measures were investigated by using these models. Different economic models were developed to perform an economic evaluation of WDM/WC measures. WDM/WC measures were evaluated in terms of its economic feasibility. Economical evaluations of WDM/WC measures were also done as an alternative to the upgrading of infrastructure. In the last evaluation, the financing of WDM/WC measures through the deferral of capital cost, was investigated. Case studies from literature, where costs as well as water savings were available, were used to evaluate these WDM/WC measures by using the developed economic models. Cost estimates for the upgrading of infrastructure, to supply an equal amount of water as the water saving achieved in each case study, were done. These estimates were used to compare WDM/WC measure with the upgrading of infrastructure. / AFRIKAANSE OPSOMMING: Daar word al hoe meer druk op bestaande hulpbronne geplaas om voldoende water te lewer. Die fokus skuif na effektiewe bestuur van hierdie hulpbronne. Wateraanvraagbestuur/ Waterbewaring (WAB/WB) projekte word geïmplementeer om krisisse van water tekorte aan te spreek en tyd te wen om nuwe hulpbronne te ontwikkel. Dit is wel moontlik om WAB/WB in geïntegreerde waterbron bestuur in te sluit en WAB/WB as ʼn ekonomiese alternatief tot kapitale investering aan te wend. Om die ekonomiese aspekte van WAB/WB te ondersoek, is daar op bestaande ekonomiese evaluerings metodes gefokus om verskillende opsies met mekaar te vergelyk. Uit die literatuur is gevind dat die belangrikste aspekte vir die ontleding van WAB/WB alternatiewe i.t.v. hul ekonomiese waarde, die koste van implementering van die WAB/WB alternatief is en die waterbesparing wat deur die implementering van die WAB/WB alternatief verkry word. WAB/WB modelle is ontwikkel om die verwagte water besparing van bepaalde WAB/WB alternatiewe te beraam. Die moontlike ekonomiese impak van bepaalde WAB/WB alternatiewe is deur die gebruik van hierdie modelle ondersoek. Ekonomiese evaluerings modelle is opgestel om WAB/WB alternatiewe te ontleed. WAB/WB alternatiewe kan as ʼn ekonomiese haalbare projek geïmplementeer word waar die kostes van die waterbesparings meer as die kapitale koste van die projek is. WAB/WB alternatiewe kan ook meer ekonomies as die ontwikkeling van nuwe bronne of opgradering van ʼn bestaande netwerk wees. Laastens is die moontlikheid om WAB/WB as ʼn alternatief te finansier deur die besparing wat bereik kan word deur ʼn kapitale projek uit te stel, ondersoek. Gevalle studies uit die literatuur, waar die kostes en waterbesparings bekend is, is ontleed deur van hierdie ekonomiese evaluerings modelle gebruik te maak. Vir elk van die gevalle studies is ʼn koste vir die opgradering van die infrastruktuur beraam om die ekwivalente hoeveelheid water te voorsien as wat deur die WAB/WB alternatief bespaar is.

A water distribution system (WDS) design deals with achieving the desired network performance. WDS design can involve new and / or existing network redesigns in order to keep up with the required service performance. Very often, WDS design is expensive, which encourages cost effectiveness in the required investments. Moreover, WDS design is associated with adverse environmental implications such as greenhouse gas (GHG) emissions due to energy consumption. GHGs are associated with global warming and climate change. Climate change is generally understood to cause reduction in water available at the sources and increase water demand. Urbanization that takes into account factors such as demographics (population ageing, household occupancy rates, etc.) and other activities are associated with water demand changes. In addition to the aforementioned issues, the challenge of meeting the required hydraulic performance of WDSs is worsened by the uncertainties that are associated with WDS parameters (e.g., future water demand). With all the factors mentioned here, mitigation and adaptive measures are considered essential to improve WDS performance in the long-term planning horizon. In this thesis, different formulations of a WDS design methodologies aimed at mitigating or adapting the systems to the effects of future changes such as those of climate change and urbanization are explored. Cost effective WDS designs that mitigate climate change by reducing GHG emissions have been investigated. Also, water demand management (DM) intervention measures, i.e., domestic rainwater harvesting (RWH) systems and water saving appliance schemes (WSASs) have been incorporated in the design of WDSs in an attempt to mitigate, adapt to or counteract the likely effects of future climate change and urbanization. Furthermore, flexibility has been introduced in the long-term WDS design under future uncertainty. The flexible methodology is adaptable to uncertain WDS parameters (i.e., future water demand in this thesis) thereby improving the WDS economic cost and hydraulic performance (resilience). The methodology is also complimented by strategically incorporating DM measures to further enhance the WDS performance under water demand uncertainty. The new methodologies presented in this thesis were successfully tested on case studies. Finally, conclusions and recommendations for possible further research work are made. There are potential benefits (e.g., cost savings, additional resilience, and lower GHG emissions) of incorporating an environmental objective and DM interventions in WDS design. Flexibility and DM interventions add value in the design of WDSs under uncertainty.

If policymakers address water scarcity with the demand-oriented approach, the income elasticity of water demand is of pivotal importance. Its estimates, however, differ considerably. We collect 307 estimates of the income elasticity of water demand reported in 62 studies, codify 31 variables describing the estimation design, and employ Bayesian model averaging to address model uncertainty inherent to any meta-analysis. The studies were published between 1972 and 2015, which means that this meta-analysis covers a longer period of time than two previous meta-analyses on this topic combined. Our results suggest that income elasticity estimates for developed countries do not significantly differ from income elasticity estimates for developing countries and that different estimation techniques do not systematically produce different values of the income elasticity of water demand. We find evidence of publication selection bias in the literature on the income elasticity of water demand with the use of both graphical and regression analysis. We correct the estimates for publication selection bias and estimate the true effect beyond bias, which reaches approximately 0.2. 1

Cette thèse étudie les liens entre développement et changement climatique dans les pays méditerranéens afin de mieux comprendre les processus et les interactions spécifiquement en jeux dans cette région, en particuliers dans les pays du Maghreb et du Mashrek. Dans le chapitre 1, nous étudions l’état des connaissances scientifiques sur le changement climatique au niveau global et au niveau méditerranéen. Cela nous permet d’aborder le problème des projections climatiques et d’analyser les résultats pour le bassin méditerranéen. Sur cette base, dans le chapitre 2, en rapprochant les projections de changement climatique et le contexte local du développement, nous mettons en évidence une vulnérabilité relativement plus élevée des pays méditerranéens en développement. Nous analysons dans le chapitre 3, les méthodes et outils permettant d’appréhender le coût du changement climatique et en déduisons des enseignements pour les pays méditerranéens. Afin d’aller plus loin dans la caractérisation et la compréhension des mécanismes en jeux au niveau méditerranéen, nous proposons, dans le chapitre 4, des approches économétriques en longue période sur données de panel de l’impact des variables climatiques sur d’une part le niveau de PIB par tête et d’autre part les rendements céréaliers. Les résultats mettent en évidence que même les économies des pays riches du bassin méditerranéen sont sensibles aux tendances climatiques, au moins sur la période 1950-2000, bien qu’ils le soient beaucoup moins que les pays en développement de la rive Sud et Est. Par ailleurs, nous confirmons que l’agriculture est un canal de diffusion majeur des effets du changement climatique dans l’économie, en particulier dans les pays en développement. La question de l’eau apparait centrale dans le traitement de l’adaptation au changement climatique. Ainsi, dans le chapitre 5, nous analysons l’état de la ressource en eau, les modes de gouvernance actuels et les options d’adaptation qui s’offrent aux pays arides. Nous présentons un exercice de simulation des demandes futures par secteur dans les pays d’Afrique du Nord, ce qui nous permet d’obtenir des ordres de grandeur sur les bénéfices à attendre des différentes options de politique qui pourront être suivies par les pouvoirs publics. Nous montrons que la gestion de la demande en eau est un des leviers déterminants de l’adaptation au changement climatique dans les pays méditerranéens et que sa mise en œuvre repose avant tout sur des réformes de gouvernance. / This thesis studies the links between development and climate change in Mediterranean countries to better understand the processes and interactions in specific games in the region, particularly in the Maghreb and the Mashreq. In Chapter 1, we review the state of scientific knowledge on climate change at global level and at Mediterranean level. This allows us to address the problem of climate projections and analyze the results for the Mediterranean. On this basis, in Chapter 2, by comparing the projections of climate change and the local context of development, we highlight a relatively higher vulnerability of the developing Mediterranean countries. We discuss in Chapter 3, methods and tools to estimate the economic cost of climate change and deduce lessons for the Mediterranean countries. To go further in the characterization and understanding of the mechanisms at play in the Mediterranean, we propose, in Chapter 4, econometric approaches using long term panel data. We test the impact of climate variables on, first, the level of GDP per capita and, second, on cereal yields. The results show that even rich Mediterranean countries are sensitive to climate change - at least over the period 1950-2000 - although much less than Southern and Eastern developing countries of the Mediterranean basin. Furthermore, we confirm that agriculture is a major channel of climate change impact in the economy, particularly in developing countries. The issue of water appears in a key parameter in adaptation to climate change. Thus, in Chapter 5, we analyze the state of water resources, the existing modes of governance and adaptation options available to Mediterranean arid countries. We present a simulation of future demands by sector in North Africa, enabling us to obtain orders of magnitude of the expected benefits of different policy options that can be followed by the government. We show that water demand management is one of the key tools to adapt to climate change in Mediterranean countries and that its implementation depends primarily on governance reforms.

<p>Economics is about the management of scare resources. In agricultural production, water stress and excess heat are the main constraints. The three essays of this dissertation try to improve our understandings of how climate and water resources interact with agricultural markets, and how global changes in agricultural markets may affect water resources. I construct empirical and simulation models to explain the interplay between agriculture and water. These models integrate economic theories with environmental sciences to analyze the hydroclimatic and economic information at different geospatial scales in a changing climate. </p> <p>In the first essay, I illustrate how irrigation, as a potential adaptation channel, can reduce the volatility of crop yields and year-on-year variations caused by the projected heat stress. This work includes estimation of yield response to climate variation for irrigated and rainfed crops; and global projections of change in the mean and the variation of crop yields. I use my estimated response function to project future yield variations using NASA NEX-GDDP climate data. I show that the impact of heat stress on rainfed corn is around twice as big as irrigated practices. </p> <p>In the second essay, I establish a framework for estimating the value of soil moisture for rainfed production. This framework is an extension of Schlenker and Roberts (2009) model enabled by the detailed soil moisture information available from the Water Balance Model (WBM). An important contribution is the introduction of a cumulative yield production function considering the daily interaction of heat and soil moisture. I use this framework to investigate the impacts of soil moisture on corn yields in the United States. However, this framework can be used for the valuation of other ecosystem services at daily basis.</p> <p>In the third essay, I have constructed a model that explains how the global market economy interacts with local land and water resources. This helps us to broaden the scope of global to local analysis of systems sustainability. I have employed SIMPLE-G-W (a Simplified International Model of agricultural Prices, Land use, and the Environment- Gridded Water version) to explain the reallocation across regions. The model is based on a cost minimization behavior for irrigation technology choice for around 75,000 grid cells in the United States constrained by water rights, water availability, and quasi-irreversibility of groundwater supply. This model is used to examine the vulnerability of US land and water resources from global changes.</p>

Water shortage issues have been growing concerns in many cities around the world in recent years, especially in Eastern cities of Australia, which is the driest continent on the earth. The aim of this PhD thesis is a development of a model to study the use of waste incineration energy supplemented by alternative energy to power seawater desalination. It is to aid the freshwater supply of a drought stricken city in Eastern Australia. My work contributes to a development of efficient model in a simpler understandable way to reduce efforts required for modelling complex multi domain problems. This research is motivated by the successive severe drought conditions that affected many Australian cities in the past few years, compounded with an additional strain from a fast growing population. While we dump our waste into the Australian landscape, in more densely populated cities in Europe and Asia, the waste is incinerated to obtain thermal energy for various purposes. The waste is used as an energy source while at the same time reducing the amount of space needed for landfill. Seawater desalination has been uccessfully practiced for quite some time particularly in the Middle Eastern countries. To deal with increasing water shortage crisis, many cities around the world have opted or are considering seawater desalination to supplement their freshwater supply. The combination of both - waste incineration and seawater desalination - has rarely been studied. This is a twofold problem that requires modelling the problem of water demand and supply together with waste incineration to find a sustainable solution. This is a complex task. The effort needed for this can be reduced by using a modelling approach that is more efficient than the traditionally used statistical approaches. In this thesis, I present a comprehensive model developed using a dynamic system approach combined with artificial neural networks. It simulates water demand and supply as well as the possible amount of the desalinated water that can be produced using the energy from clean city waste incineration. This is done while taking in various influential factors including population growth and irregular weather patterns. This research comprises a literature review on seawater desalination and waste incineration, the establishment of water demand and supply dynamics of Gold Coast City as my case study and identifying any modelling difficulties that need to be overcome. This is followed by the development of a comprehensive model and its components, model calibration and simulation experiments. It was found that with the energy of waste incineration, up to 60% of the freshwater demand could be fulfilled by seawater desalination in a sustainable way.

A falta de dados hidrológicos é fator limitante da representação mais precisa do comportamento hídrico, comprometendo a gestão de bacias hidrográficas. Quando estas bacias são responsáveis pelo abastecimento publico a situação torna-se crítica. Este trabalho tem como objetivo desenvolver uma metodologia para avaliação da disponibilidade hídrica para o abastecimento, utilizando cenários adaptados ao clima do cerrado, mesmo com carência de dados hidrometeorológicos, sendo aplicada na Sub-bacia do Ribeirão Taquarussu Grande em Palmas-TO. A proposta de metodologia consiste na Estimava da Oferta Hídrica, onde propôs obter os dados de disponibilidade hídrica através dos Métodos de Proporção de Área, de Regressão e do modelo chuva-vazão Win_IPH II, posteriormente adotando a Q90 e a Q7,10 como as vazões de referência; na Estimativa da Demanda e Projeções, que identificou os usos consultivos e a taxa de crescimento da população urbana e rural, da criação animal e os seus respectivos consumos per capita, necessária para a projeção de demanda futura; nos Cenários Propostos, foram aplicadas simulações para atendimento do abastecimento publico no horizonte de 20 anos, considerando a variabilidade climática na região e/ou inserção de novos usuários, no qual a vazão de referência adotada foi cotejada com a curva de demanda, avaliando a disponibilidade hídrica e identificando a variação do máximo déficit. Os resultados obtidos foram que a metodologia proposta se mostrou adequada, como uma ferramenta de analise e tomadas de decisões no gerenciamento integrado dos usos dos recursos hídricos; observou que a Q90 e a Q7,10 anual adotada restringe o uso da água na maior parte do tempo, enquanto a Q90 e a Q7,10 mensal possui uma maior capacidade de disponibilizar água; o maior usuário da Sub-bacia do Ribeirão Taquarussu Grande é a população urbana do município de Palmas, sendo esta responsável por 98,5% do total consumido; nos cenários, o Caso 01 do Cenário 02, demonstrou ser a tendência futura no atendimento da demanda de 66% da população urbana (ETA 006) utilizando a Q90 mensal, tendo o déficit de 47,17% no ano de 2010. / The lack of hydrological data is a limitante factor of the most precise representation of the hydric behaviour, compromising the management of hydrological basins, when these basins are responsible for the publish supply the situation becomes critical.This paper proposes a methodology for assessment of watershed conditions in the supply scenarios adapted to the scarcity of hydrometeorological data, being applied in the sub-basin of the Great Stream Taquarussu Palmas-TO.The proposed methodology is the estimate of Water Supply, which aimed to obtain data on water availability through the methods of Area Ratio, Regression and model rainfall-runoff Win_IPH II, later adopting the Q90 and Q7,10 as the flow of reference; Estimation of the Demand and Projections, which identified the uses advisory and the growth rate of urban and rural population of the animal creation and their respective per capita, which is necessary for the projection of future demand, in the proposed scenario, simulations were applied to attend the public supply in the 20-year horizon, given the climate variability in the region and / or adding new users, in which the reference flow used was checked against the demand curve, assessing water availability and identifying the shift of the maximum deficit and Estimated Cost of Work, which has proposed alternatives to increase water availability by estimating the costs of these works. The results were that the proposed methodology was adequate as a tool for analysis and decision making in integrated management of water resources uses; noted that the Q90 and Q7,10 adopted restricts the annual water use in most of the time , While the Q90 and Q7,10 monthly has a greater capacity to provide water, the biggest user of the Sub-basin Taquarussu Ribeirão Grande is the Palmas city urban population which is responsible for 98.5% of total consumption, in the scenarios, the case 01 of Scenario 02, proved to be the future trend in meeting demand of 66% of urban population (ETA 006) monthly using the Q90, with the deficit of 47.17% in 2010.

A água, apesar de ser um bem essencial para a sobrevivência, é também um bem que possui valor econômico, uma vez que, dado o uso intenso desse recurso, o mesmo passou a ser escasso. O conceito moderno de valor, em termos econômicos, considera o valor de uso como medida de referência. Dessa forma, uma maneira de evitar o uso intenso e não eficiente da água, seja pela indústria, pela agricultura ou pelo uso urbano, garantindo o seu valor econômico, é estabelecer uma medida de valor que reflita a disposição a pagar pelo uso desse recurso. Na bacia do rio Gravataí, atualmente, paga-se apenas pelo serviço de distribuição da água, nada é cobrado ainda pelo seu valor econômico. Contudo, uma vez que a cobrança pelo uso da água passou a ser estabelecida por lei (LF 9.433/97 e LE 10.350/94), algumas bacias vêm realizando estudos e estabelecendo a cobrança pelo uso da água. Dessa forma, o presente estudo busca obter um valor de referência pelo uso da água na agricultura na bacia do Gravataí utilizando-se dois métodos distintos: Método Econométrico Tradicional de estimação da demanda por água, aplicando-se a elasticidade-preço da demanda para chegar ao valor, e o Método de Valoração Contingente, que utiliza-se da Disposição a Pagar (DAP) para calcular o valor econômico da água. Para tanto, foi realizada uma pesquisa de campo nos municípios de Viamão e de Santo Antônio da Patrulha, utilizando-se por base um estudo das Nações Unidas (QUEISS, T.; SHDEED K.; GABR, M.; 2000). / Water, although it is an essential god for surviving, it is also a god that has economic value, once, given the intensive use of this resource, it is scarce. The modern concept of value, in economic terms, considers the value of the use as a reference measurement. Therefore, in order to avoid the intensive and inefficient use of water, in the industry as well as in agricultural and urban use, guaranteeing its economic value, is to establish a value measure that reflect the willingness to pay for this resource. Currently one pays only for the service of water distribution, and nothing is charged for its economic value at Gravataí River Basin. However, once the collection for the water’s use was established in law (Federal Law 9.433/97 and State Law 10.350/94), some basins are carrying out studies and stabling the collection for the water’s use. Thus, the present study aims at delivering a reference value for the water’s use in agriculture at Gravataí basin using two distinct methods: The traditional Econometric Method of demand estimation, applying the elasticity-price of demand in order to get the value, and The Contingent Valuation Method, which is used with the Willingness to Pay (WTP) to calculate the economic value of the water. According to these methods a field research in the cities of Viamão and Santo Antônio da Patrulha were carried out, using a study of the United Nations (QUEISS, T.; SHDEED, K.; GABR, M., 2000) as basis.