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We confirm that, usually, the feasibility of RWH systems is determined by the use of traditional methods based on discounted cash flow (DCF) analysis; the payback approach is the technique most used. This usage is due to the simplicity of its application. However, the use of this indicator to determine the feasibility may present some flaws, as it does not consider the period after the recovery of the initial investment and has difficulty in defining the length of time for which the investment is regarded as feasible. Moreover, this technique is not considered appropriate when it has to compare more than one investment option; however, it is this analysis that is made in many articles. However, according to Table 3, we can confirm that most of the selected publications used more than one method of economic evaluation in their studies.

Table 3

Review of the papers on the economic feasibility of RWH systems

ReferenceLocationMethodResultsWater savings (%)UsesDiscount rateLifetime (years)Price of waterIncrease of water price
Chilton et al. (2000)  Greenwich, England Payback 4 to 12 years 18.5 to 23.7 Toilet flushing   0.94 £/m³  
Chiu & Liaw (2008)  Taipei, Taiwan BCR 0.86 to 1.22  Toilet flushing 3% per year 25 17 NT$/m³  
Ghisi et al. (2009)  Brasília, Brazil NPV −4,155.45 to 24,744.64 R$ 7.4 to 57.2 Washing vehicles 1% per month 15     
Payback 31 to 165 months 
Zhang et al. (2009a) 4 cities, Australia Payback 8.6 to 21.9 years 7 to 32.3 Non-potable uses 6.5% per year  0.81 $AU/m³  
Farreny et al. (2011)  Granollers, Spain NPV −868.304 to 447.599 € 35.7 to 43.9 Laundry 0 and 3% per year 60 1.12 and 4 €/m³   
Payback 27 to more than 60 years 
Khastagir & Jayasuriya (2011)  Greater Melbourne, Australia Payback 14 to 46 years  Toilet flushing, laundry and irrigation 5 to 10% per year 40 0.9 to 1.4 $/m³  
Moreira Neto et al. (2012)  Confins, Brazil NPV −1,057,200.24 to 1,022,141.17 US$ 66 to 100 Toilet flushing, cleaning and irrigation 1% per month 30 2.36 US$/m³ 6% per year 
Payback 1.4 to >30 years 
Yoshino et al. (2013)  Belém, Brazil NPV −39,096.14 to −36,526.13 R$ 16.53 and 30.88 Toilet flushing 13.28% per year 20     
Payback more than 20 years 
Morales-Pinzón et al. (2014)  16 cities, Spain NPV −2,370.6 to 612.1 € 8 to 96 Laundry 5% per year 50 0.85 to 2.65 €/m³ 3% per year 
BCR 0.1 to 3.1 
Payback 5.5 to 204 years 
Kim et al. (2014)  Jeonju South Korea ROA Option value: US$998,000  Toilet flushing 5.14% per year 35 $ 1.26 5.09% per year 
Silva et al. (2015)  Porto and Almada, Portugal Payback 14.137 to 27.035 years 17 to 95 Toilet flushing, laundry and irrigation  50   
ReferenceLocationMethodResultsWater savings (%)UsesDiscount rateLifetime (years)Price of waterIncrease of water price
Chilton et al. (2000)  Greenwich, England Payback 4 to 12 years 18.5 to 23.7 Toilet flushing   0.94 £/m³  
Chiu & Liaw (2008)  Taipei, Taiwan BCR 0.86 to 1.22  Toilet flushing 3% per year 25 17 NT$/m³  
Ghisi et al. (2009)  Brasília, Brazil NPV −4,155.45 to 24,744.64 R$ 7.4 to 57.2 Washing vehicles 1% per month 15     
Payback 31 to 165 months 
Zhang et al. (2009a) 4 cities, Australia Payback 8.6 to 21.9 years 7 to 32.3 Non-potable uses 6.5% per year  0.81 $AU/m³  
Farreny et al. (2011)  Granollers, Spain NPV −868.304 to 447.599 € 35.7 to 43.9 Laundry 0 and 3% per year 60 1.12 and 4 €/m³   
Payback 27 to more than 60 years 
Khastagir & Jayasuriya (2011)  Greater Melbourne, Australia Payback 14 to 46 years  Toilet flushing, laundry and irrigation 5 to 10% per year 40 0.9 to 1.4 $/m³  
Moreira Neto et al. (2012)  Confins, Brazil NPV −1,057,200.24 to 1,022,141.17 US$ 66 to 100 Toilet flushing, cleaning and irrigation 1% per month 30 2.36 US$/m³ 6% per year 
Payback 1.4 to >30 years 
Yoshino et al. (2013)  Belém, Brazil NPV −39,096.14 to −36,526.13 R$ 16.53 and 30.88 Toilet flushing 13.28% per year 20     
Payback more than 20 years 
Morales-Pinzón et al. (2014)  16 cities, Spain NPV −2,370.6 to 612.1 € 8 to 96 Laundry 5% per year 50 0.85 to 2.65 €/m³ 3% per year 
BCR 0.1 to 3.1 
Payback 5.5 to 204 years 
Kim et al. (2014)  Jeonju South Korea ROA Option value: US$998,000  Toilet flushing 5.14% per year 35 $ 1.26 5.09% per year 
Silva et al. (2015)  Porto and Almada, Portugal Payback 14.137 to 27.035 years 17 to 95 Toilet flushing, laundry and irrigation  50   

NPV, net present value; BCR, benefit-cost ratio; ROA, real options analysis.

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