irrigation with wastewater combined with desalination - CiteSeerX

Int. J. Water, Vol. 4, No. 1, 2008

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A model for integrated water resources management in water-scarce regions: irrigation with wastewater combined with desalination processes Nava Haruvy* Netanya Academic College, 1 University Street, Netanya 42365, Israel E-mail: [email protected] *Corresponding author

Sarit Shalhevet SustainEcon, 126 Thorndike Street, Brookline, MA 02446, USA E-mail: [email protected]

Yehuda Bachmat Hadassah Academic College, 37 Haneviim St. Jerusalem 91010, Israel E-mail: [email protected] Abstract: We have developed a model for planning water supply from diverse sources, including groundwater, the National Water Carrier, wastewater and seawater. The model integrates hydrological, technological and economic considerations, and estimates the economic and environmental impacts of alternative water management policies; it was implemented in a case study of the Emek Heffer and northern Sharon regions in Israel. A unique hydrological database was constructed and a hydrological model was developed for planning water resources use and forecasting the chloride concentration in the aquifer. The costs of desalination processes and of the water supply to the region under various scenarios were estimated. The results include recommendations for the water treatment level and for desalination of different water sources, and forecasts of the implementation costs. We conclude that the economic cost of improving the quality of the supplied water and of the aquifer water should be considered in decision making. Keywords: groundwater salinity; multi-disciplinary model; economics; desalination; wastewater. Reference to this paper should be made as follows: Haruvy, N., Shalhevet, S. and Bachmat, Y. (2008) ‘A model for integrated water resources management in water-scarce regions: irrigation with wastewater combined with desalination processes’, Int. J. Water, Vol. 4, No. 1, pp.25–40. Biographical notes: Nava Haruvy is a Senior Professor of Economics in the Netanya Academic College, and Deputy Dean of the College’s School of Insurance. She received her PhD in Economics from the Technion in Israel. She has conducted extensive research, teaching and consulting, managed Copyright © 2008 Inderscience Enterprises Ltd.

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N. Haruvy, S. Shalhevet and Y. Bachmat research projects for competitive funds in Israel and internationally, advised decision makers in Israel and around the world, and co-directed a NATO-sponsored workshop on wastewater treatment and reuse. Her research interests focus on the economics and management of natural resources and the environment. She has published several book chapters and a large number of papers in international journals, and presented in many international conferences. Sarit Shalhevet is an Environmental Economics Consultant in Brookline, Massachusetts. She received her MBA from the Tel Aviv University in Israel, and has worked for more than a decade as an agricultural and environmental research economist at the Agricultural Research Organisation in Israel. Her research interests include ecological economics, sustainable agriculture, water and wastewater economics, and planning of open spaces. She has participated in many national and international research projects, and has published book chapters as well as papers in international journals and conference proceedings. Yehuda Bachmat is a Hydrological Consultant and a Former Director of the Hydrological Service in Israel. He teaches at the Program of Environmental Studies at The Hebrew University of Jerusalem and at the Department of Environmental Health at the Hadassah Academic College in Jerusalem. His research interests are groundwater and hydrological modelling, and he has published many reports and papers and co-authored several books on these subjects.

1

Introduction

Israel is a developed, water-scarce country, mostly characterised as arid or semi-arid. To address the problem of increasing water scarcity, Israel has increasingly adopted water desalination and irrigation with treated wastewater. However, the increased level of irrigation with wastewater has accelerated the buildup of groundwater salinity. Yaron et al. (1999, 2000) described the problem of salination for a general hydrological cell, and also the acceleration of salination caused by irrigation with wastewater. Haruvy et al. (2001) used a model based on agricultural and urban water consumption to estimate the economic implications of salination. This model was developed and implemented in a large variety of case studies in Israel. Haruvy et al. (2000) described the environmental impacts of urban development on groundwater salinity, and later (Haruvy et al., 2004) described the economic and managerial implications of the impact of wastewater irrigation on groundwater salinity, under a number of scenarios. Haruvy (2006) described the impacts of various desalination methods on groundwater salinity and costs, and Haruvy and Shalhevet (2005) described a model for minimising the environmental damages by addressing the needed changes in salinity thresholds. The present paper describes a combined planning-hydrological-technologicaleconomic model for sustainable water resource management; it enables planning of the supply and desalination of water from various sources, including groundwater, the National Water Carrier, wastewater and seawater.

A model for integrated water resources management in water-scarce regions

2

27

Methodology

We developed a combined planning-hydrological-technological-economic model for sustainable water resource management. It enables planning of the supply and desalination of water from a variety of sources, including groundwater, the National Water Carrier, wastewater and seawater. The combined model assumes given initial salinity levels in the various water resources, and predetermined quality thresholds for water supplied to the towns and/or agriculture and/or the aquifer. Desalination is initiated when the salinity of the supplied water exceeds the predetermined threshold, and the desalinated water is mixed with water from additional sources to maintain salinity at the threshold level. The model was run under several scenarios, including different thresholds (for supply to the city, agriculture or the aquifer), irrigation with and without wastewater, and various pumping policies. We compared several means of water desalination for the various scenarios in order to choose those with relatively low costs and salinity levels. Two sectors require water: towns and agriculture. Their water supplies comprise local aquifer water, imported aquifer water, National Carrier water, wastewater (for agriculture) and desalinated sea water (for domestic use). We estimated the total water demand for given region, as divided among eight hydrological cells that were based on a set of maps, agricultural crops, population size, DU – domestic water demand, and DA – agricultural water demand. We defined the quantities of water and the salinity levels for the two water-consuming sectors – urban and agricultural – as shown in Table 1. Table 1

Definitions of water quantities and salinity levels Water quantity Town (U)

Agriculture (A)

Local aquifer (L)

QLU

QLA

Imported aquifer (M)

QMU = 0

QMA = 0

Salinity level Total QL (calculated)

Initial

Current

SLO

SLI

SMO

SMI

National carrier water (N) QNU

QNA

QN

SNO

SNI

Wastewater (W)

QWU = 0

QWA (given)

QW

SWO

SWI

Seawater (O)

QOU

QOA = 0

QO

SOO

SOI

Rain (R)

QRU

QRA

SRO

SRI

Total water demand

DU

DA

Total water leaching

LWU

LWA

Total salt leaching

LSU

LSA

In addition to vertical leaching there is lateral flow, denoted by LWL – lateral water flow. Desalination is initiated when the salinity threshold for town and/or agriculture is reached, at which point SAU and SAA denote the urban and agricultural salinity levels, respectively.

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N. Haruvy, S. Shalhevet and Y. Bachmat

Urban water demand (DU) is satisfied from the various water sources, including desalinated sea water (1)

QLU +QMU +QNU +QOU = DU .

Agricultural water demand (Da) is given by (2)

QLA +QMA +QNA +QWA = DA .

The aquifer is balanced (when irrigation equals leaching) according to (3)

QLU +QLA = LWU + LWA + LWL = QL .

The water supplied from the various sources is divided as follows. If there is priority to agriculture for receiving groundwater, then for each hydrological cell QLA = max( DA − QWA , QL ).

(4)

QLU = QL − QLA .

(5)

The additional amount needed is supplied from the other water sources, mainly the National Water Carrier. For given water sources and salinity levels (as chloride – mg/l) we used a hydrological model (Haruvy et al., forthcoming) to estimate the temporal salinity levels. We assumed urban and/or agricultural salinity levels – SAU and SAA, respectively: Urban salinity level (6)

SAU = S LI QLU + S MI QMU + S N.I QNU + SOI QOU .

Agricultural salinity level (7)

SAA = S LI QLU + S MI QMA + S N.I QNA + SWI QWA .

Desalination will be initiated when the urban salinity level SAU and/or the agricultural salinity level SAA exceed their threshold values. We compared the application of several desalination methods, based on reverse osmosis: to the National Carrier water, aquifer saline water, system water, wastewater, and seawater. Designations of treated water quantities and salinity levels appear in Table 2. Table 2

Treated water quantities and salinity levels

Water source Aquifer

Water quantity Treated water quantity Salinity level Salinity treatment level QQ

QQT

SQ

SQT

National carrier

QN

QNT

SN

SNT

Wastewater

QW

QWT

SW

SWT

Seawater

QO

QOT

SO

SOT


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For example, salinity level SAU = SAA = SS. From the equation showing balance of salts, assuming desalination relates to the national carrier or aquifer, we can determine the quantities to be desalinated for each sector. The balance of salts is given by (QN − QNT ) S N +QNT S NT + (QQ − QQT ) SQ +QQT SQT = (QN +QQ ) S S .

(8)

QN S N +QQ SQ − QN S S − QL S S = QNT ( S N − S NT ) +QQT ( SQ − SQT )

(9)

Hence

or QN ( S N − S S ) + ( SQ − S S ) = QNT ( S N − S NT ) +QQT ( SQ − SQT ).

(10)

We can determine the quantity of water from each water source that needs to be desalinated: •

For desalination of groundwater alone, the amount of desalinated water is QQT =

•

( SQ − SQT )

(11)

For desalination of National Carrier water alone, the amount to be desalinated is QNT =

•

QN ( S N − S S ) + ( SQ − S S )

QN ( S N − S S ) + ( SQ − S S ) ( S N − S NT )

(12)

For desalination of wastewater QN S A + (QW − QWT ) SW +QWT SWT = (QN +QW ) S S

(13)

or QN ( S A − S S ) +QW ( SW − S S ) = QWT ( SW − SWT )

(14)

The amount of wastewater to be desalinated is QWT =

•

QN ( S A − S S ) + QW ( SW − S S ) ( SW − SWT )

(15)

For desalination of seawater For comparing salinity levels we get QO SO +QN S N +QQ SQ = (QO +QN ) S S

(16)

or QO SO +QN S N +QQ SQ = QO S S +QN S S + S S .

(17)

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N. Haruvy, S. Shalhevet and Y. Bachmat Hence, the amount of seawater supplied is QN ( S N − S S ) + ( SQ − S S )

QO =

( S S − SO )

(18)

.

The costs of various desalination processes were calculated by application of technological estimation methods to the relevant desalination processes. The designations of prices and costs for various water sources appear in Table 3. Table 3

Prices and costs of water sources

Water source Aquifer

Water quantity

Price of water source

Treated water quantity

Average cost of desalination

QQ

PQ

QQT

PQT

National carrier

QN

PN

QNT

PNT

Wastewater

QW

PW

QWT

PWT

Seawater

QO

PO

QOT

POT

We calculated the total cost of supplying water on the basis of the costs of desalination processes. CTU: Total cost of urban water supply is CTU = (QQU − QQTU ) PL +QQTU PPT + (QNT − QNTU ) PN +QNTU PNT +QOU POT

(19)

CTA: Total cost of agricultural water supply is CTA = (QQA − QQTA ) PQ +QQTA PPT + (QNT − QNTA ) PN +QNTA PNT + (QWT − QWTA ) PW +QWTA PWT

(20)

The discounted cost is C. The total discounted cost for 100 years is CTU +CTA y y=1 (1+ r )

100

C=!

(21)

where r is the interest rate. We hypothesised several scenarios, differentiated by variables that included: salinity threshold, priority of groundwater supply, and use of wastewater. For these scenarios we calculated the costs when the various desalination processes were applied. We compared these scenarios and alternatives to find the best alternatives, represented by the lowest costs.

3

Application

We applied the model to a case study area in Israel, which included the hydrological cells of Emek Heffer (cells 14, 34, 54 and 74), and the northern Sharon (cells 15, 35, 55 and 75). The eight hydrological cells were defined according to the method used by the Israeli Hydrological Service. These hydrological cells lie between Hadera and Netanya (Figure 1 and Table 4).

A model for integrated water resources management in water-scarce regions Figure 1

Map of Israel

Source: Map courtesy of CIA World Factbook, www.cia.gov

31

32 Table 4

N. Haruvy, S. Shalhevet and Y. Bachmat Description of hydrological cells

Distance from the sea (km)

Coastal cell

Western cell

West-east cell

Eastern cell

1

5

9

15 |

Emek Heffer region

14

34

54

74

| ! 6 km !

Northern Sharon region

15

35

55

75

| |

The Emek Heffer cells include the area of the Emek Heffer Regional Council which contains 26 agricultural settlements and about 30,000 residents. This area is characterised by extensive irrigation with wastewater – 12.4 MCM (million cubic metres), and high salinity in its aquifer – chlorides at over 230 mg/l. The cells of the northern Sharon include the areas of several regional councils (among them: Lev Hasharon and Hof Hasharon), as well as regional councils that include the city of Netanya, with about 150,000 residents. This area has very little irrigation with wastewater – 3.4 MCM, and low aquifer salinity – chlorides up to 164 mg/l. The Netanya wastewater plant is the source of most of the wastewater used for irrigation in the Emek Heffer settlements. We took into account the existing situation in the area and its surroundings, when we collected the data for the reported cells. We used the planning information to study the area allocations of water, water uses by the various sectors, and the water sources in the relevant hydrological cells. For the sake of simplicity of the model, we assumed that the data for water demand will remain constant over time. These data formed the inputs for the hydrological model, which predicted the temporal changes in the threshold and the salinity, and for the technological model, which examined the relevant desalination technologies and their costs. The results yielded by the hydrological and technological models were used as inputs for the economic model, which evaluated and compared the amount of desalination and the costs incurred under the various scenarios. The process of collecting the agricultural and urban data was difficult, because the required information is not available for each hydrological cell separately. The cell boundaries are straight lines that divide the mapped area vertically and horizontally into square cells, without considering natural geographic divisions or the administrative boundaries of the settlements. We produced a unique information system for the hydrological cells, based on a set of maps that include descriptions the areas – the physical area of the settlements, built-up area, areas occupied by citrus and other orchards (Table 5) – and of water sources, i.e., pumping, Water National Carrier, wastewater, and wells. We calculated the water sources and uses accordingly (Table 6).

A model for integrated water resources management in water-scarce regions Table 5

Areas (thousands of hectares)

Area

Emek Heffer

Northern Sharon

Total agricultural

8.24

8.28

Built-up

1.02

1.14

Citrus orchards

1.21

2.89

Other orchards

0.96

1.05

Field crops (remaining area)

5.30

3.19

Urban total

0.11

7.87

Total

8.30

16.16

Table 6

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Water sources and uses (MCM) Emek Heffer

Urban demand Agricultural demand – freshwater Total demand for freshwater

Northern Sharon

Total

2.576

24.718

27.294

9.637

31.357

40.994

12.213

56.075

68.288

Pumping (given)

6.780

39.504

46.284

National carrier water (computed)

7.707

17.213

24.920

Total supply of freshwater

14.487

56.717

71.204

Wastewater (given)

12.403

3.375

15.778

The hydrological model represents the coastal aquifer in the areas of Emek Heffer and northern Sharon in the form of a system divided into eight rectangular cells that correspond to the reporting cells used by the Israeli Hydrological Services. Each cell is shaped like a straight-sided box that extends from the ground surface to the base of the aquifer, and that includes two levels: the upper level represents the unsaturated zone, and it extends from the ground surface to the upper surface of the aquifer; the bottom cell represents the saturated zone, and it extends from the upper surface to the base of the aquifer. The water consumption is designated for two sectors – town and agriculture – which receive two kinds of water – freshwater and wastewater. The supply in each cell is equal to the demand. The hydrological model receives hydrological and planning data as inputs, over a predetermined period, each cell yields an output that includes the water balance, the chloride mass, and forecasts of the water balances and chloride concentrations in the saturated zone. The hydrological model was adjusted to consider the flow model parameters, equations of the annual balance of the chloride mass, and sensitivity analyses that took into account the thickness of the mixing area relative to that of the aquifer, and a linear approximation to the chloride concentration profile. We examined several scenarios that include the following supply, pumping, and allocation policies: a supply policy based on determination of thresholds for the town and/or agriculture or for the aquifer; a pumping policy based on priority of pumped water allocation given to agriculture or the town, and irrigation with or without wastewater; and a pumping policy based on pumping capacity or minimum costs.

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Several scenarios were compared. Under the basic scenario – Scenario 1 – the town threshold chlorides concentration is set at 250 mg/l. The primary priority is given to supplying water from local sources, i.e., by pumping from wells within the cell area, within the limit of their pumping capacity, and subject to the constraint of the total annual extraction from the aquifer in that area. The shortfall in the volume of water needed to satisfy the demand is supplemented by the Mekorot company (the Israeli national water company), and the water consumers in the coastal cells receive their water only from Mekorot. Agriculture receives pumping priority, and there is irrigation with wastewater. Table 7 presents the estimated allocation of water supplies under this scenario. Table 7

Estimate of water allocation according to pumping capacity, under Scenario 1 (MCM) Agriculture

Cell

Pumping

Emek Heffer

9.41

Town

National carrier

Total

Pumping

National carrier

Pumping

National carrier

2.55

0.02

11.96

0.24

0.22

Northern Sharon

21.38

9.96

14.93

9.77

36.32

19.74

Total

30.80

10.19

17.49

9.80

48.29

19.99

Percentage

75%

25%

64%

71%

29%

36%

In addition to the basic scenario, we ran several other scenarios that differed in their thresholds and their pumping and allocation policies. Scenarios 2–4 include thresholds not only for the town but also for agriculture, at the chloride levels of 250 mg/l, 150 mg/l and 50 mg/l, respectively. Scenarios 5–8 include irrigation with or without wastewater, with priority of pumped water supply to the town or to agriculture. Scenarios 7 and 8 allow irrigation with wastewater, whereas Scenarios 5 and 6 have the same salinity restrictions but do not include irrigation with wastewater. For each scenario we calculated the water allocation according to the pumping policy. The scenarios are summarised in Table 8. Table 8

Description of the scenarios Salinity threshold (chlorides – mg/l)

Scenario

Town

Agriculture

Wastewater

Priority in pumping

1

250

–

+

Agriculture

2

250

250

+

Agriculture

3

150

150

+

Agriculture

4

50

50

+

Agriculture

7

250

–

6

250

–

8

250

–

5

250

–

+; high salinity Agriculture –

Agriculture

+; high salinity Town –

Town


35

Figure 2 presents the scenarios in a graphic form. Figure 2

4

Scenarios of salinity thresholds (mgl Cl)

Results

Figures 3 and 4 depict the development of chlorides concentration through time, for the basic scenario – Scenario 1 – in the Emek Heffer and northern Sharon cells, respectively. One can see the increases in salinity levels through time, except for the coastal cell, in which no pumping is allowed. Figure 3

Chlorides concentration in Emek Heffer cells (Scenario 1)

36 Figure 4

N. Haruvy, S. Shalhevet and Y. Bachmat Chlorides concentration in Northern Sharon cells (Scenario 1)

We examined the forecast aquifer salinity levels in the 100th year, as yielded by the model runs, (Table 9) in order to compare the effects of the various scenarios. Table 9

Chloride concentration in groundwater in the 100th year (mg/l)

Cell

1

2

3

4

6

7

Town threshold chloride (250 mg/l)

Additional agriculture threshold chloride (250 mg/l)

14

310

189

210

137

232

370

34

846

459

364

182

741

1016

54

497

358

243

110

418

644

74

Medium Low threshold threshold chloride chloride Without High-salinity (150 mg/l) (50 mg/l) wastewater wastewater

1192

841

690

364

1639

1485

Emek Heffer

716

453

357

182

716

907

15

180

115

159

122

161

192

35

132

150

116

75

133

143

55

100

102

94

66

91

112

75

739

654

438

222

693

760

Northern Sharon

158

159

130

84

157

174

Table 9 presents the decrease in salinity in the 100th year for the various scenarios. The numbers correspond to progression through the scenarios, from Scenario 1 with a chloride threshold of 250 mg/l for the town alone, through Scenario 2, which includes a threshold of 250 mg/l for agriculture as well, through Scenario 3 in which the thresholds


37

are lowered to 150 mg/l, and to Scenario 4 in which the thresholds were lowered to 50 mg/l. This is emphasised in Figure 5, which depict the development in hydrological cell 54. The stricter the threshold, the lower the time-related salinity levels. Figure 5

Chlorides concentration for various scenarios (cell 54)

We also compared Scenario 6, without wastewater irrigation, with Scenario 7, that included irrigation with high-salinity wastewater. In Emek Heffer irrigation without wastewater results in a salinity (chloride) level in the 100th year that is lower by 191 mg/l (Table 9). Several different desalination technologies were integrated into the model in order to evaluate the relevant alternatives and resulting costs. The costs of desalination are influenced by various parameters such as the size of the plant, the quality of the feed water, and the location of the plant, and also by planning data that include: return on investment; components of expenses; plant availability; and costs of energy, membranes, chemicals, manpower, maintenance and overheads. The input data include: the water throughput, the quality of the feedwater, the quality of the product, capacity, drilling depth, piping distance, height of use points above the desalination plant, and water collection area. The feeds considered for desalination by reverse osmosis include: brackish water, system water, wastewater (whose costs include those of pre-treatments such as tertiary treatment and pre-membrane treatment), and seawater. Costing of these processes assumed that they would be integrated with the national water system, for which they were considered for use mainly as an additional water source. The average costs of desalination, as functions of representative initial conditions, are shown in Table 10: in the Emek Heffer area the cost of desalinating brackish water is 36 US cents/CM, that of desalinating National Carrier water is 29.4 US cents/CM (depending on the plant size),

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that of desalinating waste water is 41.6 US cents/CM, and that of seawater desalination is 54.2 US cents/CM (for a plant producing 50 MCM/year). Table 10

Average cost of desalination (US cents/CM) Brackish

System

Wastewater

Seawater

Infrastructure

13.0

14.6

3.3

32.5

Desalination

23.0

14.8

38.3

21.7

Total

36.0

29.4

41.6

54.2

From the economical point of view, we estimated the total costs of supplying water to a mixed urban and agricultural area, under the different scenarios. The inputs include the water sources according to the planning model, the forecasts of chloride concentration in various years under each scenario, as obtained from the hydrological model, and the costs of the water sources, as obtained from the technological cost budgets. For each scenario we calculated the relevant costs of the water supply for the aggregate of the Emek Heffer cells (cells 14, 34, 54, 74). Tables 11 and 12 present the accompanying total and annual costs as calculated for the various scenarios. Table 11

Calculated net present value of the total cost over 100 years (million NIS*)

Scenario

1

2

3

4

6

Town threshold

Agricultural threshold

Medium threshold

Low threshold

No wastewater

Brackish Cost increase relative to previous scenario Wastewater

380.75

404.24

482.31

876.76

518.29

–

23.49

78.07

394.45

–

–

710.74

866.85

986.78

–

Seawater

385.76

828.35

1413.95

1569.86

529.42

Desalination of

*NIS = New Israeli Shekels ($1 = NIS 4). Table 12

Calculated net present value of the annual cost (million NIS)

Scenario

1

2

3

4

6

Town threshold

Agricultural threshold

Medium threshold

Low threshold

No wastewater

Desalination of Brackish Cost increase relative to previous scenario Wastewater Seawater

19.93 – – 21.04

22.17

30.20

42.52

23.37

2.24

10.27

22.59

–

35.83

41.58

47.33

–

62.07

68.10

75.30

46.48


39

Under Scenario 1 (chloride concentration threshold of 250 mg/l determined only for the town, and no wastewater irrigation) – the annual cost ranges from NIS 19.93 million for brackish water desalination up to NIS 21.04 million for seawater desalination. Under Scenario 2 (chloride concentration thresholds of 250 mg/l for both town and agriculture) the annual cost ranges from NIS 22.17 million for brackish water desalination, through 35.83 million for wastewater desalination, and up to NIS 62.07 million for seawater desalination. Under Scenario 3 (thresholds of 150 mg/l for both town and agriculture) the annual cost ranges from NIS 30.20 million for brackish water desalination, through NIS 41.58 million for wastewater desalination, and up to NIS 68.10 million for seawater desalination. Under Scenario 4 (thresholds of 50 mg/l for both town and agriculture) the annual cost ranges from NIS 42.52 million for brackish water desalination, through NIS 47.33 million for wastewater desalination, and up to NIS 75.30 million for seawater desalination. It is evident that under all the scenarios the lowest desalinations costs are for National Carrier water, followed by brackish water, wastewater and seawater. It should be noted that seawater desalination is meant mainly to increase the total water supply, and therefore the cost of desalinating seawater in order to improve water quality includes only the marginal costs.

4

Conclusions

We constructed a unique database for the hydrological cells of the Emek Heffer and northern Sharon regions, and developed and ran a hydrological model for planning the allocation of the water resources and forecasting the concentration of chlorides in the aquifer. We also estimated the costs of various desalination processes under the regional conditions, and calculated the costs of the water supply to the region under several different scenarios. The conclusions from calculating the costs of improving the threshold chloride levels in the water supplies to city and/or agriculture or the steady-state levels in the aquifer are that desalination of brackish water involves the lowest costs; desalination of National Carrier water is effective when there is large-scale use; desalination of wastewater is significant for maintaining the chloride concentration threshold in water for agriculture; and desalination of seawater is recommended when it makes an important contribution to maintaining the national water balance. It is important to note that improving the quality of the supplied water and the aquifer water comes at an economic cost, which should be considered in decision making

Acknowledgements The paper is based on a research project financed by the Israeli Water Commission. The authors wish to thank the Water Commission for financial support. Dr. Daniel Freeman from Mathematical Models, Rehovot, helped with planning and data collecting. Amnon Zefati and Kobi Harusi from Adan Technologies, Tel Aviv, calculated the technological data.

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References Haruvy, N. (2006) ‘Reuse of wastewater in agriculture – economic assessment of treatment and supply alternatives as affecting aquifer pollution’, in Morel, B. and Linkov, I. (Eds.): Environmental Security and Environmental Management: The Role of Risk Assessment, Amsterdam, Springer, pp.257–263. Haruvy, N. and Shalhevet, S. (2005) ‘Land use and water management in Israel – economic and environmental analysis of sustainable reuse of wastewater in agriculture’, ERSA Conference Papers ersa05p376, European Regional Science Association, Available at: http://ideas. repec.org/p/wiw/wiwrsa/ersa05p376.html Haruvy, N., Bachmat, Y., Shalhevet, S. and Yaron, D. (2000) ‘Effect of urban development on water quality – environmental concerns’, ERSA Conference Papers #ersa00p419, European Regional Science Association, Available at: http://ideas.repec.org/p/wiw/wiwrsa/ ersa00p419.html Haruvy, N., Shalhevet, S. and Bachmat, Y. (forthcoming) ‘Risk management of transboundary water resources: sustainable water management of Jordan River Basin Area’, International Journal of Risk Assessment and Management. Haruvy, N., Shalhevet, S. and Ravina, I. (2004) ‘Irrigation with treated wastewater in Israel – financial and managerial analysis’, Journal of Financial Management and Analysis, Vol. 17, No. 2, pp.93–102. Haruvy, N., Yaron, D., Bachmat, Y., Wallach, R. and Spector, R. (2001) ‘An approach to economic evaluation of the damages of accelerated salination of the aquifers as a result of irrigation with wastewater’, Water and Irrigation, Vol. 418, pp.16–21. Yaron, D., Bachmat, Y., Wallach, R., Mayers, S. and Haruvy, N. (1999) ‘Not ‘the age of wastewater followed by the age of desalination’ but combined wastewater and desalination’, Water and Irrigation, No. 393, pp.5–13. Yaron, D., Haruvy, N. and Mishali, D. (2000) ‘Economic considerations in the use of wastewater for irrigation’, Water and Irrigation, No. 400, pp.19–23.