Water saving effect on integrated water resource management

Resources, Conservation and Recycling 93 (2014) 50–58

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Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec

Water saving effect on integrated water resource management Hongchao Gao a , Tong Wei a , Inchio Lou b , Zhifeng Yang a , Zhenyao Shen a , Yingxia Li a,∗ a b

State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China Department of Civil and Environmental Engineering, University of Macau, Macau SAR, China

a r t i c l e

i n f o

Article history: Received 25 March 2014 Received in revised form 14 September 2014 Accepted 16 September 2014 Keywords: Customer’s preference Economic pressure (EP) End use analysis (EUA) Integrated water resource management (IWRM) Tianjin Water-saving effect

a b s t r a c t This study proposes an improved integrated water resource management (IWRM), in which water conservation was analyzed for the entire water use process. A multi-objective optimization method was applied to optimize the IWRM, which investigated the reduction of freshwater consumption and the total water supply cost. Customer’s preference for saving water and an end use analysis (EUA) was applied in the water conservation analysis. Taking Tianjin as the study area, a reduction in customer’s economic pressure (EP) was utilized to evaluate the degree of the customer’s preference for saving water. The results revealed that agriculture had a greater preference for saving water than other sectors, where as the public had the weakest motivation for saving water. Improving the transportation method could contribute 62.1% of the total water savings in the agriculture sector. The optimization of the IWRM demonstrated that the local freshwater savings would be 21.5%, and the total cost for water supplies would decrease by 13%. However, a government subsidy of 87.5 million Yuan would be needed. Additionally, by analyzing the change in the amount of water savings affected by water price, the appropriate water price increase range was suggested to be 1.5–1.7 times the original price. © 2014 Elsevier B.V. All rights reserved.

1. Introduction In recent years, urban populations have grown at such phenomenal rates (Evans and Varma, 2009) in combination with the growing scarcity and increasing competition for water across multiple sectors. In addition, climate change has altered the temperature and rainfall patterns worldwide (Miranda et al., 2011) and therefore increased the water resource stresses (Arnell et al., 2011). Today, water concern remains high on many national agendas, and water resources security is an issue that is common to some global threats (Foster and Ait-Kadi, 2012). Thus, there is an increasing global interest in an integrated water resource management (IWRM) (Horlemann and Dombrowsky, 2012), which is regarded as “a process which promotes the management of water, land and related resources, to maximize the resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems” (Wester et al., 2009). IWRM entails management of water for various purposes and therefore involves different stakeholders aiming at achieving sustainable water resources management (Ako et al., 2010). In accordance with the objectives of sustainable development,

∗ Corresponding author. Tel.: +86 10 58804585; fax: +86 10 58804585. E-mail address: [email protected] (Y. Li). http://dx.doi.org/10.1016/j.resconrec.2014.09.009 0921-3449/© 2014 Elsevier B.V. All rights reserved.

the environmental, social, and economic functions of the water cycle have to be considered and the multi-criteria decision analysis (MCDA) method was often used to support stakeholders in managing their water resources (Calizaya et al., 2010). IWRM demands the survey of large areas as well as the inclusion of the different functions of the water cycle and water utilization processes (Koch and Grünewald, 2009). However, regional differences exist in the consideration of all of these forces and conditions (Sokolov, 2006) with emphasis on different water system aspects based on the regional characteristics. For example, political nature of water management and the complexities of water resource challenges were found to be important in the local IWRM experience in Guanajuato, Mexico (Wester et al., 2009); while in Australia, the concepts of integrated urban water resources (IURM) was found to have significant impact on the total water cycle, which received increasing acceptance by the water and land development industries (Mitchell, 2006). Furthermore, there is still a need to explore the potential of modern methods, to integrate different technologies and develop an assessment framework for resources (Mo and Zhang, 2013). Multi-objective optimization method is widely used in the water resource management area which usually has multiple conflicting objectives. Although widely applied, choosing suitable objectives and finding good methodologies to achieve each objective are always challenging for a specific study. For example, Zarghami (2010) optimized three objectives of minimizing the cost, maximizing water supply and minimizing the social hazards

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with a highlight of using compromise programming method. Reddy and Kumar (2009) used an elitist-mutated multi-objective particle swarm optimization method to find effective and efficient allocations in the reservoir operation process. Instead of using more complex programming methods or cutting in from a big aspect, this research work will focus on a specific point of water conservation effect and establish a serial of methods to evaluate the water conservation effect on consumer’s preference and finally optimize the final objectives. The studies on consumer’s preferences in the decision-making process have shown that the uncertainty in a consumer’s preference may lead to different choices when no single alternative has a decisive advantage (Dhar, 1997). Certain researchers have applied this theory in their research works, whereas not many can be found in water resource management studies. For example, Beynon and Wells (2008) improved the consumers’ preference ranking by evaluating the changes related to vehicle’s emissions. Morio et al. (2013) utilized stakeholder’s preferences to determine the optimal land use configurations with certain assessment criteria. With respect to the water-saving analysis, some experts used cost effectiveness analysis (CEA) method to select policy measures to achieve the good ecological status of water bodies as prescribed by the water framework directive. CEA was used to generate a ranking of water-saving measures, according to the ratio between the equivalent annual cost and the reduction of cost impacts, and to select the measures to be included in the Program of Measures (Berbel et al., 2011). Gilg and Barr (2006) examined the social, attitudinal and behavioral composition of water saving activities, and found the links between water saving, energy conservation, green consumerism and waste management in and around the home. The water saving abilities of various end user activities have been studies by certain researchers. For example, urban residents and local residents can save up to 77% of total potable water use compared to the average 1990s household water use by applying water saving appliances (Muthukumaran et al., 2011). By installation of sprinkler system, irrigation water can be reduced up to almost 50% (Ørum et al., 2010). Rainwater are often treated and used for landscape and road clean (Gleick, 2000). Besides the non-potable uses of rainwater, there are some cases where rainwater was used for human consumptions such as roof-harvested rainwater used for potable purposes by applying a solar collector disinfection (SOCO-DIS) system (Amin and Han, 2009), and rainwater considered for clothes

Local Fresh Water Long Distance Transferred Water

Rain water

Centrralized Water Supply

Desalinated Sea Water

washing and toilet flushing in southern Brazil (Ghisi and Ferreira, 2007). This study proposes an improved IWRM that considers various actions involved in the water savings process. The improved IWRM scheme utilizes customer’s preferences to indicate the willingness of customers to save water. In addition, end use analysis (EUA) is applied for the water resource analysis. The objective of this article is to further the IWRM study through integrating water saving actions and EUA into the entire water resource management process to achieve a comprehensively better solution for society, the economy and the environment. 2. Methods 2.1. The general model framework A traditional water supply system includes water resources, a water supply pattern and water use structures (Engström et al., 1998). This study, however, establishes an improved water supply system with water conservation and provides a further explanation of water-use structures based on the EUA. To present the operation of the new water supply system clearly, a general model framework is constructed (Fig. 1). Since the major focus of this study is the water saving ability in the improved IWRM system, which does not change with time variation, water supply variations in time is not considered in the IWRM system analysis. In proposed model, various potential water resources includes local freshwater, long distance transferred water, recycled water, rainwater and desalinated sea water. Freshwater from groundwater and surface water is treated by centralized water plants to supply end users. Recycled water and desalinated seawater are supplied by related centralized water plants. At the same time, certain end users attain water resources by themselves and use the water onsite with or without simple treatment, which are defined to be decentralized water supply in this study. For example, agriculture, industries, and rural residents often extract and use groundwater by themselves. Rainwater is considered to be collected and supplied onsite only as performed by most practices in China (Qu and Ye, 2009). For all centralized and decentralized water supply infrastructures, their capacity for expansion is considered, and their cost including operation and expansion is evaluated. Additionally, a dual quality water supply is hypothesized for all users without considering its practical limitations. Therefore, recycled water

Water Use Categories

Decentralized Water supply

Water Resources

Plant Extension, Water Quality Unit Cost Potable Water Non-Potable Water Potable Water

End Use Categories End Use

Customer Urban Resident

Water Tap, Toilet, Washing clothes, Bath

Local Resident

Transportation, Irrigation

Agriculture

Non-Potable Industry Water Public

Reuse Water

landscape & road clean

Hotel, Hospital, School, Office, Business, Others

Water Conservation Analysis Use s Preference

Technology

Income&GDP, Water Price, Government Subsidy, Watersaving Cost

Water Use Efficiency,

Government Subsidy, Economic Pressure

Drainage Capital Cost Operational Cost Amount of Water Resource

51

Legend Water Supply

Non-Potable Water

Drainage

Evaluation Factors

Fig. 1. The general model framework.

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and rainwater are supposed to supply separately from other water resources, both of which are considered to be non-potable water application only. What’s more, recycled water is hypothesized to be gray water only. The details regarding water-use structures include water user categories and end use categories. Water users are classified into 6 categories according to the user’s different behaviors and water-use purposes: urban residents, rural residents, agriculture, industry, public and landscaping and road cleaning. The end-use categories are defined as follows based on related studies about the EUA (Deng et al., 2006). Urban and rural residents comprise 4 end uses: water tap, toilet, clothes washing and bathing. Agriculture comprises transportation and irrigation. The public is classified into 6 end uses: hotel, hospital, school, office, business, and other. Industry and landscape and road cleaning do not have an end use classification due to data limitations. 2.2. Multiple objective optimizations Four objectives are optimized in this study, which include: (1) minimize local freshwater consumption; (2) minimize water supply costs, including the operation and expansion capacity; (3) minimize users’ economic pressure; and (4) minimize government subsidies. Additionally, a compromise-programming model is employed because of the incommensurability of different objectives (Fattahi and Fayyaz, 2010; Zarghami, 2010). The expected maximum and minimum values of each objective are identified and used to convert the original values to a value ranging from 0 to 1 before optimizing the model. Then, the weighted sum method for these adjusted objectives is calculated. The weight of each objective (Wa ) is assumed to be a fixed value of 1. The equation is shown as follow. min F(x) =

  f max (x) − fa (x)  a a

famax (x) − famin (x)

Wa

(1)

where F(x) is the integration of the four objectives. 2.3. Water conservation analysis Water conservation is considered for all parts of the water use structures, especially for water use categories and end use categories. Each water use category is analyzed in terms of its water saving ability. The same applies to the end-use categories. There are two factors that affect water saving ability; one is the influence of the consumer’s preference for water conservation and other is the effect of technology. Customer’s preference for water conservation is always linked to particular economic factors (Fan et al., 2013), such as residents income, a city’s GDP, a government subsidy, water saving cost, and et al. These economic factors can be used to evaluate customer’s economic pressure. 2.3.1. Customer’s preference for water conservation The basic principle for rational consumers to choose certain goods is to maximize their benefits from those goods, a phenomenon applicable in many fields. Whether customers have a preference for saving water depends on associated benefits. Although the benefit for each customer is complex because it involves many factors, the economic factor, such as economic pressure, is generally the priority aspect (Flouri, 1999). A customer’s preference for saving water is incorporated into the water conservation analysis (Pavlikakis and Tsihrintzis, 2003) in this IWRM study. A customer’s income (Income) has an influence on the customer’s preference for saving water, whereas a customer’s economic pressure (EP) for water consumption is used

to demonstrate this influence. The EP is defined to be the ratio of water’s cost (Cost) to a customer’s income (Income) as shown in Eq. (2) (Olmstead and Stavins, 2009). The subscript r represents the condition with water conservation and o represents the situation without water conservation.

⎧ Costr ⎪ ⎨ EPr =

incomer

⎪ ⎩ EPo = Costo

(2)

EPreduction = EPr − EPo

(3)

incomeo

Generally, most users will present a significant water conservation preference when the actual economic pressure can be mitigated through water conservation, or when the EP exceeds a certain value. In this study, a preference indicator (W) is defined according to the various EP status as shown in Eq. (3). Specifically, water consumers will be willing to save water when the economic pressure at water conservation condition is less than that without water conservation originally.



W=

1 if EPr < EPo 0

(4)

else

where W is a binary variable that represents the customer’s preference for saving water. When W is equal to 0, customers have no preference for saving water. Otherwise the customers have a preference for saving water and the degree of the preference depends on the value of EPr 2.3.2. End use analysis EUA is applied to each user in this study. Each water user is categorized by end uses, each of which represents a certain proportion of a user’s water consumption and has a specific water saving ability (Willis et al., 2010). For example, urban residents and local residents save water by applying water saving appliances. Agriculture and industry mainly focus on reducing the water lost during transportation and improving the efficiency of irrigation and industrial usage. Public mainly relies on enhancing the public’s preference to save water. Landscape and road clean rely on using recycled water (Gleick, 2000). By analyzing each end use, different water saving characteristics were obtained, and the potential of each water customer was visually represented. 3. Case study Some preconditions were considered in the proposed water conservation model. Tianjin is subdivided into 11 regions based on the administrative division (Fig. 2). Water supply across regions is allowed with transportation costs (De Wit and Stankiewicz, 2006) determined by the unit transport cost, distance and the amount of water transported. The topography and specific layout in each region are ignored. Therefore, each region can be regarded as a connected point that contains full information. Based on the reality, desalinated seawater can only be supplied from the Bin Hai New Area and Ning He, which are close to the sea. All water transferred over long distances is reserved in local reservoirs located in Wu Qing and Bao Di. Water customers and their end uses are classified based on the description provided in Section 2.1. 4. Results The multiple effects obtained from the improved IWRM model was compared with the original water consumption condition that did not take water conservation into consideration. The comparative analysis for the two results is considered and presented.

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Table 1 Income, GDP and water prices for each regional user (Zhang et al., 2004; Yang and Abbaspour, 2007; Tianjin Statistical Yearbook 2011 (Du et al., 2012)). GDP (108 Yuan)

Income (Yuan)

Center Binhai Dong Li Xi Qing Jin Nan Bei Chen Wu Qing Bao Di Ning He Jing Hai Ji Xian Water/reuse water price (Yuan)a a

Urban resident

Rural resident

Industry

Agriculture

Public

25,016 25,743 24,609 20,538 23,239 20,630 20,630 25,348 19,271 23,990 22,380 4.4/2.2

0 14,210 14,210 14,365 12,921 14,265 11,580 11,000 11,345 10,998 10,998 4.4/2.2

1113 3433 355 370 178 335 189 120 95 196 58 7/4

0 8 4 10 4 9 29 21 21 15 21 0.8/2

1680 1589 181 147 109 120 124 100 54 68 136 7/4

The water prices are an average for all regions and all regions apply the same water price.

Table 2 Supply capacity, capital cost and operational cost of each source (Wang et al., 2008; Chu and Chen, 2009).

7

3

Capacity (10 m ) Capital cost (Yuan/m3 ) O&M cost (Yuan/m3 )

Water plant

Transfer water

Reuse water

Urban rain harvesting

Rural rain harvesting

Desalination

126.7 0.48 0.34

11 1.9 5.1

41 0.65 0.21

3.4 3.07 1.07

3.9 1.25 0.05

10.5 4.34 4.26

Additionally, the analysis of certain key parameters for saving water and the results are also explored. All necessary data have been collected from the Tianjin Statistical Yearbook (2011) (Du et al., 2012) and other related literatures presented in Fig. 3 and Tables 1–3. The data include user’s water demand and local water resources in each region. In addition, income, GDP and water prices for each regional user, the proportion of user’s water demand, and maximum non-potable water are also presented. Users water demand in each region

Fig. 3. Users’ water demand and local water resources in each region (Tianjin Water Resources Bulletin, 2012).

Table 3 Proportion of user’s water demand, maximum non-potable water.

Agriculture Transportation Irrigation Industry Resident Water Tap Toilet Wash clothes Bath Public Hotel Hospital School Office Business Other

Fig. 2. Location and sub-district of Tianjin.

Proportion (%)

Max non-potable water (%)

50 50 –

100 100 70

35 29 7 29

33 100 0 0

22 6 23 20 12 18

20 17 20 30 30 25

was determined by the social economical information such as population, GDP, etc. Non-potable water are mainly used for irrigation, toilet flushing, floor cleaning and industry usage. Due to the relative high water quality requirement of laundry water

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Fig. 4. The comparison of each objective result between the improved IWRM model and the original status.

with COD ≤ 60 mg/L (Beijing Quality and Technical Supervision, 2007) and the relative low quality of reuse water from secondary treatment of wastewater treatment plant with COD ≤ 100 mg/L, reuse water is not considered for laundry in this study.

Fig. 5. Recycled water consumption in each region from the improved IWRM model and the original status.

4.1. The overall objective comparison Each objective result of the improved IWRM model and the original water consumption status is illustrated in Fig. 4. The bars at a certain level represent one objective result from the two methods with the name and unit of the objective written to the right of the bars at the same level. Better multi-benefits were found as a result of the improved IWRM model than the original status. Local freshwater use is reduced by 21.5% (approximately 2 × 108 m3 ) due to water conservation, which can greatly relief the local water resource stress including less groundwater over extraction, less sea water desalination requirement, etc. Additionally, the average proportion of water costs of each user’s income also decreases by 12%. This result indicates that the proposed model not only contributes to local water resource protection, but water conservation can also mitigate a consumer’s economic pressure for water costs, even considering the extra cost users have to pay to replace water-saving appliances. Although approximately 87.5 million Yuan would be needed in the form of government subsidies, a more cost-effective solution would be achieved because of the significant reduction of 13% in the total cost of water supplies, which is the summation of the operational cost and capital cost for capacity expansion. 4.2. Overall water saving ability Additionally, the result obtained for recycled water consumption in each region using the original status and the improved IWRM model are compared and displayed in Fig. 5. More recycled water is utilized by industry after water conservation. As shown in Fig. 6, recycled water consumption by industry increased sharply from 3.81 × 107 m3 to 12.11 × 107 m3 . Alternatively, less recycled water was consumed by the public, urban and rural residents in the proposed model. In particular, recycled water consumption by urban residents decreased by approximately 7 × 107 m3 which was caused by the application of water saving appliances such as water saving toilets. Furthermore, there was no change in the consumption of recycled water for agriculture, landscaping and road cleaning between the two scenarios, because agriculture, landscaping and road cleaning use the recycled water in the original status. While recycled water used in Sydney, recycled water was mostly consumed in agriculture and urban water supply (Anderson, 2006). The specific results concerning water conservation in each region and for each user are shown in Fig. 6. The Bao Di area contributes the most to water conservation (approximately 9.5 × 107 m3 ). Other regions, such as Wu Qing, Ning He, Ji Xian and

Fig. 6. Water conservation distribution among regions and users.

Center also have large water savings that range from 1.5 × 107 m3 to 2.2 × 107 m3 . With the exception of the Center region, all of the other mentioned regions are located in the outer suburban areas of Tianjin. The composition of the water saving for different users is shown in Fig. 6, where the prevailing position of water savings in the agricultural sector is clearly displayed. The amount of agricultural water savings, which accounts for 82% of total water saving’s, is more than ten times that of urban residents water saving. The fact that the majority of agriculture is located in the outer suburbs explains why water conservation primarily occurs in these regions. Alternatively, the public and rural residents conserve the least amount of water, accounting for only 3% of total water savings. 4.3. Water saving ability analysis 4.3.1. Water saving ability analysis based on user willingness The EP reductions of the users in each region are illustrated in Fig. 7, which are calculated with Eq. (4). Because customer’s economic pressure has an effect on the customer’s preference for water conservation (Hearne and Salinas, 2002), and water pricing is often proposed as a way to curb water use (Agthe and Billings, 2002), we can analyze water saving potential through economic pressure reduction. Compared with other users whose economic pressures drop less than 0.2%, we observed a significant benefit for agriculture. Agriculture’s economic pressure can be substantially reduced from 0.04 to 3.49% by replacing water appliances and providing a government subsidy. Industry’s economic pressure can also experience a relatively significant reduction, especially in the City

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55

Fig. 7. Economic pressure change of each user.

Center, Ji Xian and Wu Qing. Conversely, only a minimal reduction in economic pressure reduction can be obtained for the public sector, which indicates that the public has experiences less economic pressure for water use. 4.3.2. Water saving ability analysis based on the EUA Water savings and government subsidies for each end use were analyzed further as shown in Table 4. The data in Table 4 were calculated with general methods using available statistics from “Tianjin Statistical book 2011” (Du et al., 2012) and other relevant literatures. For example, when calculating the water saving amount of toilet water saving, we used the amount of the household in Tianjin (350 × 104 households), water saving village coverage rate (14.7%), household water use in flushing toilet in Tianjin (9.49 m3 /month) (Zhang and Brown, 2005), and water-saving percentage of watersaving toilet (14%) (Ding, 2001). Multiplying these four parameters together, we obtained the water saving amount of using water saving toilet (0.82 × 107 m3 ). For the agriculture sector, approximately 11.77 × 107 m3 of water can be saved by improving the transportation method, which accounts for 62.1% of the total water savings of agriculture. In the north and northwest of China, agricultural water use efficiency is the key to mitigating water shortage and reducing environmental problems (Deng et al., 2006). However, government subsidies for transportation account for only 43.9% of that for agriculture, or 3.66 × 107 Yuan. This result indicates that agriculture can achieve better water conservation benefits by improving the transportation method. In terms of residents, replacing the water tap is the most efficient method of water conservation, whereby approximately 1.28 × 107 m3 of water can be saved with only 7 × 105 Yuan in government subsidies. Replacing toilet appliances can save approximately 0.82 × 107 m3 of water, but requires 0.29 × 107 Yuan in incentives. The least amount of water can be saved by replacing bath appliances at a cost of approximately 6 × 105 Yuan in government subsidies. Hotels, schools and office buildings can only contribute a small amount to total water conservation without government subsidies. These findings simply that the public has fewer incentives for water conservation and, furthermore, are less sensitive to financial incentives. Finally, a better, multi-aspect benefit for the entire water system, including the environment, economy and society can be achieved using the proposed improved IWRM model. For each consumer and end use, the specific water saving abilities and the

effect of government subsidies were analyzed. Among the consumers and end uses, agricultural water savings exhibits a stronger dependence on government subsidies because of its low profit. Conversely, the public water savings show little sensitivity to financial incentives. Second, the effect of water savings on the recycled water distribution is indicated in the results, in which industry takes precedence for reusing water over other uses after the implementation of a strong water savings policy. Thus, the mitigation effect of water savings and government subsidies on the users’ economic pressure was observed and analyzed. 5. Discussion 5.1. The influence of weight of each objective To explore the model’s sensitivity to the weight change of each objective, the optimization results were recalculated with the change in each weight, ranging from 0 to 0.75, and are presented in the x axis of Fig. 8. The y axis represents the output value of minF(x) in Eq. (1), which is the optimized integration of the four objectives, being uniformed with dimensionless scale. As shown in Fig. 8, the optimized multi-objective output values generally displays little variation around the estimated value in response to the weight change, signifying that the multi-objectives optimization model will produce a relatively reliable result (Deb and Gupta, 2006). Alternatively, the model result appears to undergo a large variation when the weight of the objective that represents a government subsidy is set at an extreme value. The output rises suddenly when that weight increases to 0.6 and drops gradually when that weight decreases to 0.3. This behavior indicates that the objective has a relatively large effect on the model result. This finding also implies that the attitude towards subsidizing the cost for water savings has a potentially large effect on the entire urban water system. 5.2. The influence of economics To thoroughly explore how the amount of water savings changes with the range of economic pressure, the change in water savings with a rise in water price was simulated. As shown in Fig. 9, the amount of water savings exhibits a stepped increase trend with a raise in water price. The water savings amount increases

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Table 4 Water savings and government subsidies for each end use.

Water saving (107 m3 ) Government subsidy (107 Yuan)

Water saving (107 m3 ) Government subsidy (107 Yuan)

Water tap

Toilet

Bath

Transportation

1.28 0.07

0.82 0.29

0.33 0.06

11.77 3.66

Irrigation

Hotel

School

Office building

7.18 4.67

0.23

0.33

0.03

Fig. 8. The sensitivity analysis of the model.

slowly from 23 × 107 m3 to 23.3 × 107 m3 when the water price rises to 1.5 times its present value, and then increases sharply to approximately 24.5 × 107 m3 when water price reaches 1.7 times its present value. Thus, the amount of water savings is inelastic to the water price until the price rises to 3.3 times its present value, after which the amount of water savings exhibits another rapid increase from 24.5 × 107 m3 to 26.5 × 107 m3 . As demonstrated by the results, encouraging water conservation by rising the water price can have a positive effect when the water price is raised up to 1.7 times its current value or after the price exceeds 3.3 times its current value. The results reveal an appropriate range for water price increases, and further suggest that water savings are not

Fig. 9. The change in the water-saving amount with a water price rise.

always elastic with respect to water price; simply raising the water price will not achieve decision makers’ expectations for water conservation. Alternatively, the economic pressure would still increase with a rise in water price, and the users’ economic interests would be sacrificed. Therefore, this result implies that another method that considers multiple benefits is needed, such as a government subsidy. 5.3. Discussion of limitations Some assumptions and simplification of the model limit the result of this study effect and should be improved in the future. For example, the practical water supply network and regional layout are simplified. The proportion of the dual-quality water supply is idealized without having investigated the practical conditions of such a supply. The market share of the considered appliances, the diversity of the appliances that use water and the sub-classification for industry are also not considered in the process of EUA due to data limitations. Furthermore, the dynamic interaction between the annual water demand and water supply should be analyzed in the future. Fundamentally, the proposed model attempts to compare the current water supply and water saving methods to develop a more sustainable solution for regional development and thereby reduce the negative effects of an oversupply of water on water savings. Benefits would not only occur in the form of savings on operation costs and limits on extending infrastructure, but water savings would also reduce freshwater consumption. From this perspective, water savings can be regarded as a new water resource for a large region (Dixon et al., 1999). Furthermore, in considering users’ economic pressure for water consumption and conservation,

H. Gao et al. / Resources, Conservation and Recycling 93 (2014) 50–58

the results reveal greater acceptance from each user. Additionally, the model shows that water saving contributes to reducing a city’s dependence on a centralized water supply infrastructure through reduced freshwater usage and more on-site water reuse. Finally, the results contribute to the promotion of regional water conservation development by analyzing the holistic effects of the whole system, and offer more readily available water management methods to decision makers. 6. Conclusions Water conservation ability analysis methods were built up in the improved IWRM system, which uses a multi-objective optimization model to reach the optimal solutions. EUA was implemented by using user’s economic pressure, water price and government subsidy. User’s economic pressure was applied to weigh the willingness of the customer’s water conservation. Government subsidies were used to replace water saving appliances for further water conservation. Finally, water conservation was analyzed in the entire IWRM. The IWRM application in Tianjin showed that by applying water conservation techniques the local freshwater use could be reduced by 21.5% and the average water costs of each user’s income also decreased by 12.7%. Agriculture has the greatest potential to save water, which showed a strong dependence on government subsidy due to its low profit. As a contrary, public water conservation show little sensitivity to financial incentive. Industries would take precedence for reusing water over other users after strong water saving policy. Additionally, the impact of water price on water saving is analyzed, and the cooperation between rising water price and government subsidy for promoting water saving is advised. The detailed analysis on water conservation and the related methods used in the framework of IWRM is a good reference to other researchers and the methods can be used in other regions. Although there are certain IWRM studies in other regions of the world, they usually concentrated on public participation (Ako et al., 2010), social-ecological and technical aspects etc. Water saving effect has not been well studied in the IWRM framework and this study provides a good example. Although water saving abilities have been analyzed according to different end uses and the effects have been incorporated into the overall IWRM optimization model, the real local conditions such as available lands to build storage tanks and water treatment facilities, the economic conditions that influence the government subsidies, and the later maintenance requirements etc. were not discussed in this study. Future research work might continue to focus on these issues and make the results from this study more practical and applicable to the real society. Acknowledgments This research is supported by the MYRG072(Y1-L2)-FST13-LIC and the FST Short-Term PD & VF Scheme 2013 from the University of Macao, the National Science Foundation for Innovative Research Group (Grant 51121003), and the National Science Foundation of China (Grant 51278054). The authors are grateful to these supporters. References Agthe DE, Billings RB. Water price influence on apartment complex water use. J Water Resour Plan Manage 2002;128(5):366–9. Ako AA, Eyong GET, Nkeng GE. Water resources management and integrated water resources management (IWRM) in Cameroon. Water Resour Manage 2010;24(5):871–88. Amin MT, Han MY. Roof-harvested rainwater for potable purposes: application of solar collector disinfection (SOCO-DIS). Water Res 2009;43:5225–35. Anderson JM. Integrating recycled water into urban water supply solutions. Desalination 2006;187(1):1–9.

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