Abstract

Intermittent water supply (IWS) is associated with numerous negative consequences with respect to health and access along with technical impacts that aggravate the sustainable supply of water, thus rendering Sustainable Development Goal 6.1 (SDG 6.1) hardly achievable. The gradual, or zone-by-zone, transition from IWS to continuous water supply is very effective in terms of economic scarcity. This work focused on designing a theoretical ‘hybrid’ hydraulic model where both types of services, intermittent and continuous, were included in the modelling. The preliminary, not calibrated model, which was applied in a district in Amman, has shown to be efficient on both the technical and economic sides as it achieves independent district metering areas. Sustainable access to water, however, necessitates an integrated solution taking into account the technical, economic, social and psychological factors along with the modelling aspect highlighted in this work.

INTRODUCTION

The sixth Sustainable Development Goal (SDG) states that by the end of 2030, countries should ‘ensure availability and sustainable management of water and sanitation for all’. This puts water resources under real challenge given a vital need to provide sustainable access to water while considering ongoing urban development and population growth (Hering Maag & Schnoor 2016).

Approaches that lead to new water resources or decrease in water usage by advanced technology or behavioral change are widely discussed in the literature (Lekouch et al. 2012; Mandel 2012; MacGregor et al. 2014). Decreasing water losses or nonrevenue water (NRW) within the distribution network is also a major water resource, knowing that the estimated annual global physical water loss is 32 billion m3 (Mutikanga Sharma & Vairavamoorthy 2009).

Water operators in many developing countries see intermittent water supply (IWS) as a ‘practical’ solution to cope with the increase in domestic water demand. This is an illusion, as IWS imposes various technical, social, health, and financial problems that intensify with time, leading to a vicious cycle with higher operation and management costs, more leakages, increased deterioration of the infrastructure, and thus an increase in the gap between supply and demand (Rouse 2013; Ilaya-Ayza et al. 2016; Charalambous & Laspidou 2017). For instance, a study conducted in 2012 has shown that the use of IWS in drought conditions in Lemesos, Cyprus, led to tripling the number of pipe breaks, and doubling that of service connections that have led to more water losses. The annual losses and the operating costs also remarkably increased (Charalambous & Laspidou 2017). Nonetheless, the World Health Organization considers IWS to be a major source of contamination as it imposes serious health hazards (Kumpel & Nelson 2016). IWS also limits personal freedom, especially for women who are usually in charge of collecting water for the household, and is indicative of social inequity (Caprara et al. 2009; Majuru Suhrcke & Hunter 2016).

It has been shown that the transition from IWS to continuous water supply (CWS) is achievable and, if properly managed and monitored, can lead to a decrease in the quantity of water needed. For instance, the transition to CWS in demonstration zones in Northern Karnataka, India, led to the decrease of leakage from 50% to 7% and to 18% reduction in the quantity of water supplied to the zones (Hastak et al. 2017). Similar results were also obtained in Phnom Penh, Cambodia, following water service reforming that led to the decrease of NRW from 70% to 6% (Das 2010).

However, there is little information in the literature on the transition from intermittent to CWS. This can be due to the general myth that IWS leads to less water consumption or to financial constraints; achieving CWS is extremely challenging when systems are badly degraded, thus requiring huge capital funding (Mohapatra Sargaonkar & Labhasetwar 2014).

This transition, however, is inevitable when considering the UN's definition of sustainability ‘as the direct counterpart to retrogression, or slippage, in access to water and sanitation services’ and that ‘states must develop standards and targets that take into account sustainability in the operation, maintenance and rehabilitation of services … ’ (WHO 2016). It is clear that IWS puts the achievement of SDG 6.1 under real threat in the developing countries that apply such a rationing strategy.

In the total-system approach that is usually adopted for such a transition, the whole region/district is reverted into CWS. Unfortunately, such an approach cannot be standardized as, along with the financial burden, the pace of the deterioration caused by IWS could be more rapid than the transition.

To overcome these challenges, a gradual ‘zone-by-zone’ approach is necessary where a certain district is supplied continuously with water while the surrounding districts are kept rationed. The area of CWS is then expanded stepwise until it covers the whole city. This puts less pressure on the water utility in terms of operation, maintenance, financing, and even users' opinions. Once CWS proves to be successful in a small zone, the word will spread, and users will be more willing to consider this transition and, if needed, pay extra water charges to provide a better service (Rouse 2013). However, this is not to exclude the impact of the ‘ability to pay’ along with the ‘willingness to pay’ on increasing water tariffs.

This is not the case with the total-system approach, whose outcomes take more time, leaving the users with an unclear idea about the project and its impact on improving their water access.

The gradual system is not mentioned much in the literature, with only few studies providing hydraulic models. In 2003, McIntosh recommended the gradual scheme for the transition to CWS. He emphasized that the key issue for the sustainability of such an approach lies in proper management and water billing to have a full cost recovery to enable proper operation and maintenance (McIntosh 2003).

Similarly, Seetharam also recommended the zone-by-zone transition based on observations and roundtable discussions in India (Seetharam 2005). One critical finding was that the progressive increase in the number of hours of supply is inefficient and the best way is to have a direct transition to CWS.

Myers focused on defining the different stages needed for an adequate gradual transition (Myers 2003). Dahasahasra applied the findings of Myers and developed a hydraulic model for the zone-by-zone transition to CWS in Badlapur, India. The importance of hydraulic model planning and proper zoning and isolation of the district metering areas (DMAs) were highlighted. The model included only the DMAs that would have CWS (Dahasahasra 2007).

A conceptual approach for the gradual transition, while taking into consideration the complexity of restructuring the zones and organizing the database, was reported by Klingel & Nestmann (2014). In the model described, the DMAs having CWS were assumed to receive water from independent tanks.

So at best, these studies were limited to modeling of the continuously supplied sectors within a certain region rather than having models that target both continuous and intermittent sectors at the same time.

Therefore, the aim of this research was to investigate theoretically the potential adaptations of a network analysis model for the transition from IWS to CWS using a gradual approach while including both types of services in the modeling and while considering the network's renovation rather than its full replacement.

To make this work more concrete, Amman, the capital of one of the most water-scarce countries in the world, was taken as an example.

Context

According to a UNDP Human Development Report, Jordan is one of the four most water-scarce countries in the world, with an annual water availability of 120–145 m3 per capita, which is by far less than the global average of 500 m3 per capita (Hadadin et al. 2010). The country is in water deficit in most of the regions, especially in the densely populated Amman-Zarqa (MWI 2016). A projected estimate shows that the country will still be in water deficit and water availability will be around 91 m3 per capita in 2025 excluding the influence of climate change (Hadadin et al. 2010).

Much concern is given to Amman, the capital, which holds more than 50% of the Jordanian population (UN 2017). The city has experienced a huge influx of Syrian refugees (680,000) that has put more pressure on its water utilities especially that 85% of them are living among the host communities (Ghazal 2017). This has led to an abrupt increase in demand by 20% and to an increase in water expenses by around JOD 500/refugee/year (MWI 2016).

Amman already has a rationed service where users have tanks on top of their buildings for non-potable water storage. Buying water from private vendors is very common, especially in summer, where there is a huge influx of tourists and of Jordanians returning from abroad for vacation (Rosenberg Talozi & Lund 2008).

The country decided to reallocate water to Amman by the Disi Water Conveyance Project, which brings water via 300 km pipes from the fossil Disi aquifer, which is located in the east of Jordan and is shared with Saudi Arabia (Hadadin et al. 2010). The project was put into action in 2013 and was advertised to be able to provide enough water for CWS in Amman. However, it only increased the hours of supply from 24 h a week to an average of 48 h per week (Miyahuna 2015).

Because of the shortage of new reliable water resources, Miyahuna, Amman's incorporated public water facility, and in collaboration with the German Development Bank, the French government, and USAID, has focused on the management of water losses within Amman's network since its NRW is estimated to be between 38% and 48% (Miyahuna 2015). This is done by replacing the old meters with more sensitive ultrasonic meters, renovating the distribution network, rezoning the current DMAs of the 44 district zones (DZs) of Amman, and monitoring and detecting leaks.

Taking the opportunity of the ongoing renovations, one of the renovated districts, DZ 27, was chosen in this study for developing the model needed for the transition from IWS to CWS using the zone-by-zone approach.

METHODS

A simulation approach using adapted network analysis modeling was used to determine the hydraulic feasibility of achieving gradual continuous supplies. Effectively, a separate submodel was developed for each zone within a connected model for the whole water supply area under consideration.

Data on water demand and junctions' elevations were extracted from Google Earth where the KML file provided by Engicon was uploaded on Google Earth. For each junction, the elevation determined by Google and the number of buildings supplied by this junction were recorded. Costs of rehabilitating each zone were estimated, in reference to a quote provided by Miyahuna, to assess the improved economic feasibility of a staged approach.

Description of the site

Tariq, or DZ 27, is a residential area that is part of the Greater Amman Municipality, which is located in the northeast part of Amman, with an overall population of 150,000 (Figure 1(a)) and an elevation range of 760–920 m above sea level. It is divided into seven DMAs: A1, A2, A3, B, D, E1, and E2 (Figure 1(b)), with 18,728 customers. The region is supplied with water from Tariq Reservoir, which is 959 m above sea level. This reservoir receives water via a DN 1,200 mm water main from the major water reservoir in Amman, Dabouq, which is at an altitude of 1,030 m, where all the water allocated to Amman is collected and stored. Tariq's water network, of a total length of 89.8 km, is composed of around 525 pipes of DN ranging from 1,200 mm (water main) to 63 mm within the different DMAs.

Figure 1

(a) Location of Tariq District within the Greater Amman Municipality. (b) The seven DMAs of Tariq District (provided by Miyahuna Water Company).

Figure 1

(a) Location of Tariq District within the Greater Amman Municipality. (b) The seven DMAs of Tariq District (provided by Miyahuna Water Company).

Data collection

The overview of Tariq with its water network was provided by Engicon, an engineering consulting agency, in the form of a KML file that can be viewed by Google Earth. The water pressure in Tariq varies depending on the location, but Miyahuna aimed to limit the pressure within a range of 3–9 bar so six pressure-reducing valves (PRVs) were added for this purpose. Bentley's WaterGEMS V8i, which is used by both Miyahuna and Engicon, was used to create an approximation of the current water network of Tariq with the currently allocated zones. As indicated in Figure 2, which is a screenshot of the software's representation of the current status of the different DMAs during water supply, although many households receive water with a pressure of 3–9 bars, there are junctions throughout Tariq that have pressures less than 3–9 bar (large grey nodes).

Figure 2

The overview of a hydraulic model of Tariq network with the water pressure extremes highlighted.

Figure 2

The overview of a hydraulic model of Tariq network with the water pressure extremes highlighted.

Creating a continuous supply model using zone-by-zone approach

The existing water network, which has been recently fully refurbished including pipes and water meters, was used in this theoretical study as the starting point for the transition.

Usually, for the intermittent service, the quantity of water delivered is constant at a maximum level throughout the supply period. The average water demand is equal to the instantaneous demand with no short-term spikes; thus, its hydraulic pattern would include the same level of demand with a multiplier of 1 for the whole 48 h of supply (Figure S1a, Supplementary Material). The operators at Miyahuna currently use such a pattern for the modelling and the actual delivery of water to residents and thus we also used it for the zones with IWS.

The continuous service, however, has a flow-demand variation over the day between maximums and minimums. Although it is difficult to record such variations in regions where only IWS is available, Engicon and Miyahuna isolated a district in Amman and provided it with CWS. A diurnal pattern, which is similar to the classical pattern of water usage, was obtained (Figure S1b, Supplementary Material). Different multipliers, ranging between 0.75 and 1.25 that are in accordance with the demand variation over the day, were considered to make the network capable of withstanding the short spikes in demand.

Junctions

Since water flows in Tariq by gravitation, the elevation of the junction is an important factor in determining the pressure of water flowing in it. Moreover, the number of households that are supplied from a junction should also be defined to specify the junction's water demand.

Importing the elevations of the junctions using TREX gave inaccurate values due to limited data received from the source; thus, Google Earth was used to determine the exact elevations, which were then manually inserted to WaterGEMS V8i. To simplify the task, junctions that are in close proximity were given the same elevation. Similarly, using Google Earth, the number of households that are connected to each junction were estimated and noted. Current zoning regulations for apartment buildings allow the construction of four stories, and thus each building was considered to have 10 households (with the ground floor).

Sequence of DMAs

A simplified version of the network was drawn using AutoCAD including the seven DMAs and pipes of ID greater than or equal to 150 mm (Figure 3).

Figure 3

Water network of Tariq (provided by Engicon).

Figure 3

Water network of Tariq (provided by Engicon).

Two factors were taken into consideration when determining the order of the DMAs in this transition: the level of isolation from the other zones and the number of customers. Thus, DMAs with fully independent water pipes and low numbers of customers were prioritized so that the order of upgrading was as follows: A3, A2, D, E2, B, E1, and A1. It is important to note that while water was continuously supplied to a certain DMA, the rest would have their usual access to an intermittent supply of 48 h a week.

Data entry

Seven scenarios were run, each corresponding to a stage where an additional DMA was transformed to CWS. For each junction in Tariq, one of the two patterns, diurnal or IWS, was added, along with the flow demand, which was calculated from the number of households served by this junction. After defining these values, the first scenario was run, where one zone (A3) had CWS and the rest had rationed service. Later, another scenario was run where an additional zone (A2) was considered to have CWS and the rest were rationed. The last scenario was then assessed where all the zones had CWS. In each scenario, issues regarding pressure, whether too high or insufficient, would be checked and resolved accordingly. Adding a PRV could decrease the pressure of the water flowing to a specific region, whereas increasing the flow would be the only way to improve low water pressures.

RESULTS AND DISCUSSION

Phase 1: the transition of zone A3 from IWS to CWS

The calculated quantity of water delivered to each household was 0.03 m3/h in A3, whereas the other DMAs had a water flow of 0.105 m3/h during the 48 h of supply (refer to Supplementary Material). After specifying the water quantity needed for each junction at A3, the simulation was run to check if the overall demand of water throughout the day is less than or equal to that provided by Tariq Reservoir.

After confirming that the demand at the junctions did not exceed that supplied by the reservoir, it was important to check the pressure variation during the day at all the DMAs. As expected, all the DMAs having intermittent supply did not have any significant pressure changes except for two junctions having pressure as high as 11.2 bar. However, DMA A3 had a significant increase in pressure during off-peak hours, with a high pressure range between 8.4 and 12.1 bar.

Even during the peak demand at 8:00 a.m., based on the simulation, DMA A3 received water with a pressure range between 7.5 and 11.4 bar, with the majority of junctions having pressures greater than 9 bar (Figure S2a, Supplementary Material). Since the standard criteria of pressure at each junction should be a minimum of 2.5 bar and a maximum of 9 bar (Twort et al. 1994), it was thus crucial to add a PRV to the DMA. The hydraulic model in WaterGEMS V8i that Engicon provided included a PRV at the main 150 mm pipe, which connects A3 to the water network of Tariq. However, the PRV is inactive at the current state as the DMA's pressure range is within the accepted pressure range. So the PRV was then activated, and the downstream pressure was regulated so that when the simulation was run again, the pressures at the junctions were between 9 bar and 4.2 bar during both high- and low-demand hours as indicated in Figure S2b (Supplementary Material).

Phases 2–7: gradual CWS to A2, D, E2, B, E1, and A1

Similarly, the same protocol was followed for having gradual CWS in DMAs A3 and A2 in Phase 2 and then DMAs A3, A2, and D in Phase 3. In Phases 4, 5, and 6, DMAs E2, B, and E1 were also included within the CWS service, respectively. The results of these phases are summarized in Table 1. All the simulations assessed had an equilibrium between supply and demand. Note that the values of the pressure range indicated in the table correspond to those of the DMA, which are newly provided with CWS. For instance, in Phase 2, the pressure range 6–12.7 bar corresponds to that of DMA A2.

Table 1

Summary of the results of phases 2–7

PhaseContinuously supplied DMAsWater balancePressure (bar)PRV addedPRV modifiedNew pressure (bar)
A3, A2 True 6–12.7 NA 2.8–8.7 
A3, A2, D True 4.7–10.7 2.9–8.7 
A3, A2, D, E2 True 3–8.1 NA NA NA 
A3, A2, D, E2, B True 3.9–8.9 NA 3.1–7.9 
A3, A2, D, E2, B, E1 True 3.6–11 NA 3.3–8.6 
A3, A2, D, E2, B, E1, A1(All) True 3.4–9.4 3.2–8.5 
PhaseContinuously supplied DMAsWater balancePressure (bar)PRV addedPRV modifiedNew pressure (bar)
A3, A2 True 6–12.7 NA 2.8–8.7 
A3, A2, D True 4.7–10.7 2.9–8.7 
A3, A2, D, E2 True 3–8.1 NA NA NA 
A3, A2, D, E2, B True 3.9–8.9 NA 3.1–7.9 
A3, A2, D, E2, B, E1 True 3.6–11 NA 3.3–8.6 
A3, A2, D, E2, B, E1, A1(All) True 3.4–9.4 3.2–8.5 

A total of seven new Globe PRVs would be needed for pressure management to be installed to (DN 150 mm − 200 mm) pipes entering DMAs. As for the already installed PRVs, their output pressures could be adjusted without the need for their replacement. Table S1 (Supplementary Material) includes the output pressure of each of the PRVs of Tariq District.

The final simulation of Tariq with CWS is represented in Figure 4. Almost all of the water flowing in Tariq has a pressure that follows the standard criteria (3–9 bar) even during the peak times except for that flowing from the major reservoir with pressure of 2.5 bar (large grey nodes). This is by far much better than the service's current state with respect to rationing and pressure range, where many junctions have pressures as low as 1.2 bar (Figure 2).

Figure 4

Final status of Tariq following full transition to CWS.

Figure 4

Final status of Tariq following full transition to CWS.

Discussion

The results obtained from the model designed herein show that gradual transition to CWS is theoretically achievable using an extended simulation pattern where the baseline of the diurnal water demand pattern of zones with CWS corresponds to the water demand of zones with IWS. A notable modification to the existing modeling techniques was crucial to devise the model that encompasses both types of services. During the service upgrade, Tariq's customers will continue to receive at least the same service provided before and the cost for the rehabilitation would be limited to the price of the added PRVs for pressure optimizations (around 10,000 USD).

A 15% increase in water supply (381,696 m3 per month) will be needed for the transition of Tariq, including DMA B which is currently not supplied by water, to CWS while taking into account the multiplier factor and the quantity of water to be delivered per capita (120 L/day/capita). Nonetheless, the readings of the bulk meter at Tariq Reservoir indicated that it received 386,003 m3 of water in March 2017. This shows that the quantity of water that can be provided to Tariq, in theory, exceeds that needed for CWS.

However, a limitation of the model presented is that it did not take into account the water losses between Tariq Reservoir and the customers. Before 2017, there were estimates of the NRW in Amman but nowadays according Miyahuna, every three days, a new meter is installed, making it much easier to have closer estimates of the actual NRW. For instance, the NRW of the first quarter of 2017 in Tariq was 32% so that customers receive 81.6 L/capita/day of water intermittently and thus are forced to buy water from private vendors to meet their basic needs.

Nonetheless Tariq represents a ‘best-case scenario’ as Tariq's DMAs were recently reorganized, redistributed, and isolated so that Tariq currently has seven independent DMAs instead of four highly interconnected ones and receives water from only one reservoir instead of three (Figure 5).

Figure 5

Old scheme of the piping network of Tariq (provided by Engicon).

Figure 5

Old scheme of the piping network of Tariq (provided by Engicon).

Despite focusing only on the theoretical modelling phase in this study, we represent below the major criteria for a successful transition from IWS to CWS that we drew out from our findings in Tariq, which could be replicated in different areas around the globe (Table 2).

Table 2

Main factors for proper transition from IWS to CWS

CategoryConditions
Data 
  • - Regularly updated:

    • • Elevations and Number of junctions

    • • Number of households supplied by each junction

    • • Maps of existing networks with DMAs

    • • Water supply (quantity and pattern)

    • • NRW value

    • • Water resources

    • • Water tariffs

 
Modelling 
  • - A single water source per district

  • - Rezoning of DMAs to:

    • • Adjust size

    • • Include areas of similar elevations

    • • Completely independent

 
Infrastructure 
  • - Water meters

  • - PRVs

  • - Power supply

 
Human resources 
  • - Well trained employees

 
Organizational 
  • - Management

  • - Strategy & Planning

  • - Operation & Maintenance

 
Social 
  • - Myths vs reality

  • - Behavioral change

  • - Involving public in decision making

 
Institutional (Political) 
  • - Political commitment

 
Economic resources 
  • - Funding (sustainability)

 
CategoryConditions
Data 
  • - Regularly updated:

    • • Elevations and Number of junctions

    • • Number of households supplied by each junction

    • • Maps of existing networks with DMAs

    • • Water supply (quantity and pattern)

    • • NRW value

    • • Water resources

    • • Water tariffs

 
Modelling 
  • - A single water source per district

  • - Rezoning of DMAs to:

    • • Adjust size

    • • Include areas of similar elevations

    • • Completely independent

 
Infrastructure 
  • - Water meters

  • - PRVs

  • - Power supply

 
Human resources 
  • - Well trained employees

 
Organizational 
  • - Management

  • - Strategy & Planning

  • - Operation & Maintenance

 
Social 
  • - Myths vs reality

  • - Behavioral change

  • - Involving public in decision making

 
Institutional (Political) 
  • - Political commitment

 
Economic resources 
  • - Funding (sustainability)

 

Data are an important tool for any upgrading plan; therefore, continuous updating of a reliable and coherent database is indispensable to provide theoretical models that represent actual simulation to the real situation on the ground (Myers 2003).

A recent study having the same approach presented herein but with highly interconnected 15 DMAs required a relatively complicated three-stage transition to CWS (Ilaya-Ayza et al. 2018). Thus, as indicated in this work, transition necessitates the presence of DMAs that can hydraulically operate independently, but are still part of the entire region's hydraulics (Dahasahasra 2007), with each DMA having homogeneous elevations to facilitate the water flow by gravitation. Decreasing the sizes of the DMAs was also needed to better manage water losses (Table 2).

Having the same water reservoir for both intermittent and continuous flow limits the possibility of having a shortage of supply to the customers in all the DMAs; the operator's concern will be to have enough water in this common reservoir rather than trying to provide water to multiple reservoirs at different times. This is, by far, more improved and more equitable than the case reported in 2014, where the upgraded DMAs had their own reservoirs (Klingel & Nestmann 2014).

Data collection and thus modelling would not be possible without the availability of adequate infrastructure to measure the quantity of water supplied, used and leaked and to manage pressure across the network (Table 2). Since Amman has 24/7 electricity service, energy was not a barrier to the transition to CWS. However, this is not to undermine the impact of energy, and its costs, on water services as it could hinder the upgrading process.

Other factors that also play a major role in the transition include the presence of a water operator with a clear strategy regarding operation, maintenance and management of the services. A supply-oriented strategy should dominate over a consumption-oriented strategy, especially in water-scarce countries (Klingel & Nestmann 2014). Building the capacity of these operators regularly at the institutional and individual levels should also be implemented (Table 2).

Providing sustainable CWS should also involve a ‘social transition’ where a behavioral change is adopted (Table 2). Since the customers use water ‘until their roof storage tank is empty,’ this would lead to more stress on the already-stressed water resources, as was the case in one of Amman's districts, where users realized the extra amount of water they had consumed and started to regulate their water consumption after receiving the first bill. Thus, providing CWS without informing the public during the planning process will result in problems in the functioning capability of the designed system. Ideally, for enhanced commitment, the public should be involved in decision making (Rouse 2013).

Another challenge that should be overcome at both the community and policy makers' levels is disproving the myth that CWS requires more resources than IWS (Table 2). It is then where real changes in policies and practices would take place.

The gradual transition provides a reliable solution in case of economic scarcity, as limited expenses are needed at a time. However, funding could be a major challenge for the implementation and the sustainability of achieving gradual CWS although it is of less economic burden compared to a full-scale approach (Table 2). Despite the virtuous cycle of raising tariffs in terms of sustainability and improvement of service delivery, this issue is highly critical at the national level so it is not easy to implement. However, since the prices of water from private vendors are generally higher than the operator's tariffs, it is more likely for people to be willing to pay more for a better service while still providing a lowlife tariff for the poor (McIntosh 2003; Rouse 2013). Nonetheless, willingness to pay and ability to pay studies should be done to get a definite answer.

Consequently, a feasibility study that takes into account the potential reduction in water losses, the consumer's behavioral development, and the future scenario of the CWS should be conducted prior to the transition (Aboelnga et al. 2018).

Therefore, the sustainability of the service provided following the gradual transition relies on the integrated management of water resources taking into consideration social equity, environmental sustainability, and economic efficiency. Such a transition is the only way to have sustainable water access (Purvis 2016).

Note that this theoretical study, which needs to be further validated in the future, was limited to the conditions of Tariq used by Miyahuna and Engicon as the aim was to assess the model on the currently used parameters. Thus, simulations were based on volume–dependent demand for water that flows by gravitation. However, the model should be tested in the future for other conditions like the pressure-dependent demand approach, dynamic pressure management and for water flow by pumping to confirm its applicability in different conditions. Note that for water flow by pumping, another issue might rise which is related to the availability of electricity. For instance, as is the case in Lebanon, one of the major issues for having IWS is the lack of 24/7 electricity supply in the country.

LIMITATIONS

The main limitation of this study was time, which forced the author to focus on Tariq District rather than the whole city of Amman for the transition to 24–7 supply using the zone-by-zone approach.

Another major limitation was the inability to import the junction elevations from Google Earth to WaterGEMS V8i. The author had to mark the coordinates of each elevation and manually insert the values to the software. Similarly, though most of the data needed was provided by Miyahuna and Engicon, the water demand at each junction couldn't be provided, and the author estimated the water demand on each junction by determining the number of households supplied by this junction. Both tasks using Google Earth were time-consuming, which makes it very challenging to apply the model on areas with larger populations.

The author could not acquire detailed numerical data about the future water projects of Amman. The analysis and possible future scenarios would have been more precise if coupled with numerical estimates of the quantities of water to be delivered.

CONCLUSION

A theoretical hybrid hydraulic model that favors a balanced coexistence of intermittent and continuous water services during the gradual transition is designed in this work. The case study used for applying this model was in one of the most water-stressed cities in the world, Amman, with a district of seven zones.

The approach is to model the system so that a zone can be ‘isolated’ and upgraded to achieve CWS without affecting the remainder of the system. The demand of the surrounding zones is also included within the demand pattern of the upgraded zone to maintain the formers' access to the service. The model is then developed to move to achieving CWS in the next zone, and so on until the complete system has been remodeled to achieve CWS throughout.

The theoretical hybrid model designed proved to be adequate for an improved service during the zone-by-zone transition to CWS. More importantly, it was shown that CWS can be achieved without any additional water resources and especially that the water demand increase can be compensated by reducing the network's water loss, whose value exceeds that needed for the CWS. The study dismisses the general ‘myth’ that CWS requires more resources.

It is also very important that the psychological aspects are addressed. People in charge should believe that CWS is actually possible for progress to be made. The results of this study should be promoted to achieve that belief.

Although the zone-by-zone approach has been theoretically demonstrated in Amman, this new approach once validated, with its designed hybrid model, can be considered to be widely applicable as a simple and affordable way to meet SDG 6.1.

ACKNOWLEDGEMENTS

The authors would like to thank Mr Bambos Charalambous for making valuable connections, and the NRW teams at Miyahuna and Engicon for providing data and assistance.

FUNDING

This work was supported by the University of Oxford, School of Geography and the Environment, and Kellogg College. The funders had no role in study design or article preparation.

CONFLICTS OF INTEREST

The authors declare no conflict of interest.

SUPPLEMENTARY MATERIAL

The Supplementary Material for this paper is available online at https://dx.doi.org/10.2166/ws.2019.142.

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