High non-revenue water (NRW) values as a percentage of system input volume form a serious problem that many water utilities worldwide have to confront nowadays. There are ways to mitigate the effect by adopting strategies with short- and long-term results. Water pressure management (PM) is one of the most efficient and effective NRW reduction strategies. To calculate pressure management of economic level of leakage (ELL), several steps have to be taken, such as full water costing, calculation of economic benefits and losses of PM interventions and definition of the related investment's break-even point. In this paper, the results of these three procedures required to define the ELL level are analyzed, in order to present the way they are linked together. The water distribution system of Kozani city (in Northern Greece) is used as the case study network. The results of both the net present values PM implementation results and the investment's break-even estimation are analyzed.

## INTRODUCTION

During the last decade, water utilities have moved towards the implementation of pressure management (PM) to reduce the high non-revenue water (NRW) values from which their systems are suffering. Βy reducing excessive pressure, real loss components (background leakage, reported and unreported leaks) are reduced. In fact, the volume of the last two components is reduced not only due to pressure reduction, but also as bursts frequency (breakage rate) is being reduced also. New breaks rate depends on the maximum operating pressures of the network. District metered area (DMA) implementation and pressure reducing valves (PRVs) installation are strong leakage management tools with positive effects on water systems management (Farley & Trow 2003; Thornton *et al.* 2008; Puust *et al.* 2010). PM implementation leads to reduced leakage flow rates and bursts repair costs both for mains and service connection pipes (McKenzie *et al.* 2004; Babel *et al.* 2009). Τhe anxiety of revenue loss related to a network's reduced operating pressure and the difficulty to predict the economic benefits and losses, prevented water utilities implementing PM projects (Kanakoudis & Gonelas 2015a). There have been several efforts recently promoting pressure and leakage management as policies achieving both water savings and conservative demand and also delaying infrastructure expansion (Girard & Stewart 2007; Fantozzi & Lambert 2007). A PM project starts by dividing the entire network into smaller ‘hydraulically isolated’ areas (DMAs) for easier and more effective/efficient management and inspection. PRVs are installed near DMA entering nodes to restrain excessive pressure and thus ultimately reduce real losses.

Optimal formation of DMAs and installation of PRVs can be achieved by testing scenarios developed in a calibrated and validated network's hydraulic simulation model. DMA formation is a multi-dimensional problem and there have been many efforts to solve it using optimization techniques (Deuerlein 2008; Di Nardo *et al.* 2013). Searching for the optimal (in terms of cost–benefit analysis) level of PM investments is a complex process too. PM's economic level of leakage (ELL) estimation requires calculation of the full water cost through breakdown of the water utility's Balance Sheet. Then the economic benefits and losses caused separately by each PM intervention should be safely calculated. Finally the break-even of the investment must be defined too. This methodology is analyzed and implemented in the water distribution system (WDS) of the city of Kozani's WDS. The formation of 24 DMAs and installation of 12 PRVs were simulated in the WDS's hydraulic model. The impact of five PM scenarios was estimated and the net present value (NPV) of PM implementation was calculated considering both economic benefits and costs (revenue losses considered too) arising from the network's pressure reduction. Break-even of the PM investments proved to be crucial for estimating the EARL (economic annual real losses) level. The NPVs and the break-even of the PM investments were all determined. For a more accurate analysis, two economic benefits approaches were applied, the direct benefit approach (resulting from reduced energy, treatment and maintenance costs) and indirect benefit approach (resulting from reduced personnel, insurance and vehicles operation costs). Finally, the calculation of the system input volume (SIV) reduction rate depending on the network's operating pressure is presented.

## METHODOLOGY

To safely calculate the ELL for any PM scenario, there are three prerequisites. At first it is necessary to correctly analyze the full water cost demonstrating its variation during the PM scenario implemented. Then, the reliable calculation of economic losses and benefits resulting from the PM scenario must follow. Finally, the EARL levels must be safely assessed, defining the balancing point between PM's total costs and revenues.

### Full water costing

WFD 2000/60/EC requires the calculation of the three full water cost components (direct, resource and environmental cost – DC, RC and EC). In 2013, the authors presented a respective methodology, suggesting the full analysis of the water utility's Balance Sheet in various sub-costs (Kanakoudis & Gonelas 2013). Based on that methodology, the Balance Sheet is split into 11 operation and maintenance sub-costs and three capital sub-costs (Table 1). Furthermore, each one of these sub-costs is allocated to the seven urban water procedures (Table 2). This water cost breakdown in parts, helps in the calculation of economic benefits and losses, resulting from PM interventions.

Operation & maintenance costs . |
---|

Personnel cost |

Energy cost |

Leasing and rents |

Maintenance cost |

Consumables cost |

Insurance cost |

Telecommunications cost |

Vehicles operating cost |

Taxation cost |

Financial cost |

Management cost |

Capital costs |

New investments |

Depreciation cost |

Capital (opportunity) cost |

Operation & maintenance costs . |
---|

Personnel cost |

Energy cost |

Leasing and rents |

Maintenance cost |

Consumables cost |

Insurance cost |

Telecommunications cost |

Vehicles operating cost |

Taxation cost |

Financial cost |

Management cost |

Capital costs |

New investments |

Depreciation cost |

Capital (opportunity) cost |

Urban water procedures . |
---|

Abstraction |

Supply |

Raw water treatment |

Storage |

Distribution |

Drainage & sewage water treatment |

Administration |

Urban water procedures . |
---|

Abstraction |

Supply |

Raw water treatment |

Storage |

Distribution |

Drainage & sewage water treatment |

Administration |

### Economic benefits, expenditures and revenue losses resulting from a PM scenario

Regarding PM results, it was found that due to the SIV reduction, the energy cost of abstraction, supply, treatment, storage and distribution of water is reduced. Raw water treatment consumables cost (chemicals, chlorine, etc.) is reduced too. Reduction of a network's pressure results in fewer pipe breaks and therefore lower maintenance and related infrastructure replacement costs. Lambert *et al.* (2013) estimated the correlation between the decreased maximum pressure in a network and the reduced rate of new breaks. Subsequently, both the personnel and vehicle operation costs needed to repair the decreased number of breaks are reduced too. Kanakoudis & Gonelas (2015a) proposed equations that calculate several economic benefits resulting from new-break rate reduction due to pressure reduction.

Equipment purchase and installation costs occurring at the beginning of the investment are accounted as PM expenditures. Other expenditures are PM interventions management and maintenance costs and cost of studies (Kanakoudis & Gonelas 2015a). Pressure reduction results in revenue losses for the water utility due the reduced metered water volume (as a part of it, is pressure dependent). These revenue losses are calculated utilizing the network's hydraulic model, which is able to simulate the nodal consumptions as pressure dependent. This means that the pressure dependent rate of billed water consumption volume should be determined first.

### Calculating the investment's break-even

^{3}], is the total cost of the interventions [M€] for achieving the specific SIV reduction, and are the coefficients resulting from the correlation, is the total cost of the initial interventions [M€], is an index equal to in integers [M€], is the cost of interventions beyond which does not vary [M€], is an index equal to in integers [M€] and is a reduction factor and depends on caused by the initial interventions.

## IMPLEMENTATION

### Basic characteristics of Kozani's WDS and its hydraulic model

^{3}. There are three pressure zones formed: (a) a limited higher zone to the north (altitude ranging from +750 to +800); (b) a middle zone (altitude ranging from +710 to +750); and (c) a low zone to the south (altitude ranging from +610 to +710), covering 60% of the total water demand (Figure 2).

### DEYAK's full water costing

### Implementation of the PM scenarios and calculation of their NPVs

Kozani's WDS was divided into 24 DMAs (Kanakoudis *et al.* 2014). The basic criteria taken into account were hydraulic efficiency and meeting firefighting requirements for each DMA. Five basic PM interventions/scenarios were prioritized and successively implemented. These scenarios were mainly based on installing a number of PRVs at the entrances of some DMAs (Kanakoudis & Gonelas 2015a). The application of the *n*th intervention implies the implementation of the (*n*−1)th intervention. Table 3 shows the reduction of the SIV caused by forming the DMAs and each one of five PM successive interventions.

Water savings . | |||||
---|---|---|---|---|---|

PM interventions . | (m^{3}/year)
. | % SIV . | PM interventions . | (m^{3}/year)
. | % SIV . |

DMA formation | 125,112 | 1.71 | 3rd intervention | 156,476 | 2.26 |

1st intervention | 1,460,786 | 19.97 | 4th intervention | 164,954 | 2.38 |

2nd intervention | 231,603 | 3.32 | 5th intervention | 137,018 | 1.98 |

Total | 2,275,948 | 31.65 |

Water savings . | |||||
---|---|---|---|---|---|

PM interventions . | (m^{3}/year)
. | % SIV . | PM interventions . | (m^{3}/year)
. | % SIV . |

DMA formation | 125,112 | 1.71 | 3rd intervention | 156,476 | 2.26 |

1st intervention | 1,460,786 | 19.97 | 4th intervention | 164,954 | 2.38 |

2nd intervention | 231,603 | 3.32 | 5th intervention | 137,018 | 1.98 |

Total | 2,275,948 | 31.65 |

^{3}, while after all PM scenarios were implemented it dropped to 4,645,439 m

^{3}. According to the second approach, economic benefits also included the reduction of personnel, insurance and vehicles operation costs related to breaks and leaks repairing (Figure 5). These costs are considered as indirect benefits.

### Break-even calculation

Interventions . | SIV . | SIV reduction . | Cost per intervention . | Accumulated cost after each intervention . | |
---|---|---|---|---|---|

(m^{3}/day)
. | (m^{3}/day)
. | (m^{3}/year)
. | (€) . | (€) . | |

1st intervention | 12,405.58 | 4,345.11 | 1,585,965 | 150,240 € | 150,240 € |

2nd intervention | 11,771.05 | 4,979.64 | 1,817,569 | 107,427 € | 257,667 € |

3rd intervention | 11,342.35 | 5,408.34 | 1,974,044 | 136,408 € | 394,075 € |

4th intervention | 10,798.08 | 5,952.61 | 2,172,703 | 179,674 € | 573,749 € |

5th intervention | 10,423.20 | 6,327.49 | 2,309,534 | 349,165 € | 922,914 € |

Interventions . | SIV . | SIV reduction . | Cost per intervention . | Accumulated cost after each intervention . | |
---|---|---|---|---|---|

(m^{3}/day)
. | (m^{3}/day)
. | (m^{3}/year)
. | (€) . | (€) . | |

1st intervention | 12,405.58 | 4,345.11 | 1,585,965 | 150,240 € | 150,240 € |

2nd intervention | 11,771.05 | 4,979.64 | 1,817,569 | 107,427 € | 257,667 € |

3rd intervention | 11,342.35 | 5,408.34 | 1,974,044 | 136,408 € | 394,075 € |

4th intervention | 10,798.08 | 5,952.61 | 2,172,703 | 179,674 € | 573,749 € |

5th intervention | 10,423.20 | 6,327.49 | 2,309,534 | 349,165 € | 922,914 € |

Equation (2) calculates the annual SIV reduction when PM reduces the current annual real losses (CARL) to the EARL levels. Table 5 presents the reduced SIVs for different NPV time reference periods and for direct and overall (direct and indirect) economic benefits. When overall economic benefits are considered, more PM interventions are cost-effective. Thus, overall economic benefit consideration increases the profit of each PM intervention, so there is more cash available for further (new) PM interventions to be applied, resulting in higher SIV reduction.

NPVs time reference . | SIV reduction (m^{3})
. | |
---|---|---|

Direct economic benefit . | Overall economic benefit . | |

5-years | 2,241,167 | 2,650,703 |

10-years | 2,534,420 | 2,815,867 |

15-years | 2,644,605 | 2,881,703 |

NPVs time reference . | SIV reduction (m^{3})
. | |
---|---|---|

Direct economic benefit . | Overall economic benefit . | |

5-years | 2,241,167 | 2,650,703 |

10-years | 2,534,420 | 2,815,867 |

15-years | 2,644,605 | 2,881,703 |

### Correlation of Q _{REV} reduction as % of R _{SIV} in relation to pressure

*P*is pressure (kPa).

SIV components . | Water volumes . | |
---|---|---|

Initial Status . | PM implementation in EARL level (direct and indirect benefit) . | |

SIV | 6,921,387 | 4,039,684 |

Billed consumption | 2,555,472 | 2,159,489 |

Authorized non-billed consumption | 138,428 | 116,978 |

Illegal use | 69,214 | 58,489 |

Reading errors | 127,774 | 107,975 |

Under-registration | 127,774 | 149,405 |

Real losses | 3,902,727 | 1,447,349 |

SIV components . | Water volumes . | |
---|---|---|

Initial Status . | PM implementation in EARL level (direct and indirect benefit) . | |

SIV | 6,921,387 | 4,039,684 |

Billed consumption | 2,555,472 | 2,159,489 |

Authorized non-billed consumption | 138,428 | 116,978 |

Illegal use | 69,214 | 58,489 |

Reading errors | 127,774 | 107,975 |

Under-registration | 127,774 | 149,405 |

Real losses | 3,902,727 | 1,447,349 |

## RESULTS AND DISCUSSION

DEYAK full water cost for 2011 (base year) was equal to 7,827,795 €, while the RC was equal to 863,761 €. The breakdown of DEYAK's Balance Sheet costs led to a more reliable calculation of economic benefits and losses related to PM scenarios applied. DMA formation and PRV installations were simulated in the network's hydraulic model. Then, the annual economic benefits and expenses were calculated for different NPV time reference periods. Reduction of burst frequency due to the reduced maximum network operating pressures led to reduced pipe breaks and therefore to direct maintenance cost reduction. NPVs of the interventions were calculated for two different approaches of economic benefit definition (direct and overall = direct + indirect). Comparing the two approaches above, NPV is almost five times higher when the overall economic benefits are considered. The NPVs of the PM scenarios after the 15-years study period range from 1,591,415€ (when only direct benefits are considered), to 6,864,564€ (when also indirect benefits are included too).

The cost of the initial five PM interventions (922,914 €) and the resulting reduction of the SIV (2,309,534 m^{3}) helped in finding the break-even of these PM investments. Using the initial interventions data and Equation (1), the reduction of SIV was calculated for any amount of cash available for PM interventions. The reduction of the SIV resulting from the PM interventions (up to the investment's break-even point) for the 15-year study period was calculated equal to 2,644,605 m^{3} and 2,881,703 m^{3} for considering direct and overall economic benefit respectively. Concerning the utility's revenue losses due to the SIV reduction (related to the pressure dependent demand), it varies with the network's operating pressure. As this pressure decreases, the rate of the reduced invoiced consumption gets lower.

## CONCLUSIONS

The most efficient impact on both real losses and billed consumption has been identified to be PM (apart from the obvious but nevertheless extremely costly one of the assets' replacement). To fully estimate the ELL of any presume management scenario, it is necessary first to calculate the full water cost, estimate the economic benefits and losses caused separately by each PM intervention and calculate the investment's break-even point. When applying lower pressures in the system, burst frequencies of distribution mains and service connections pipes are reduced. In Kozani's WDS, high values of water losses were observed, mainly due to the network's high operating pressures. Τhe economic benefits and losses of the proposed PM interventions (and DMA formation) were calculated. PM interventions were virtually (in the hydraulic model) implemented by installing a relatively small number of PRVs in specific DMAs. NPVs of 6 (DMA formation +5 PM scenarios) proposed interventions reached high values. The maximum time period reference for NPV calculation was 15 years. It was observed, as expected, that for longer NPV time period calculation, the investment's profit was getting higher, resulting in higher real losses reduction.

The calculation of revenue loss caused by the reduction of the pressure-dependent part of the actual water consumption is crucial. This will determine the reduction rate of the revenue water and therefore the utility's revenue losses level. However, NPV calculation is important during the estimation of the EARL level. In the present paper, a graphical solution of the problem detecting the break-even of the PM interventions was developed, which led to high SIV reduction. It is very important, during the quantification of the results, to calculate the *R*_{SIV} rate which expresses revenue water.