UWA Publishing

This book has been produced to give a total overview of the Activated Sludge Model (ASM) family at the start of 2000 and to give the reader easy access to the different models in their original versions. It thus presents ASM1, ASM2, ASM2d and ASM3 together for the first time. Modelling of activated sludge processes has become a common part of the design and operation of wastewater treatment plants. Today models are being used in design, control, teaching and research. Contents This title belongs to Scientific and Technical Report Series ISBN: 9781900222242 (Print) ISBN: 9781780402369 (eBook)

Available for subscribers to the IWA Publishing eBooks collection only.Over the past twenty years, the knowledge and understanding of wastewater treatment have advanced extensively and moved away from empirically-based approaches to a first principles approach embracing chemistry, microbiology, physical and bioprocess engineering, and mathematics. Many of these advances have matured to the degree that they have been codified into mathematical models for simulation with computers. For a new generation of young scientists and engineers entering the wastewater treatment profession, the quantity, complexity and diversity of these new developments can be overwhelming, particularly in developing countries where access is not readily available to advanced level tertiary education courses in wastewater treatment.This book addresses this deficiency.It assembles and integrates the postgraduate course material of a dozen or so professors from research groups around the world that have made significant contributions to the advances in wastewater treatment.The book forms part of an internet-based curriculum in wastewater treatment which also includessummarized lecture handouts of the topics covered in bookfilmed lectures by the author professorstutorial exercises for students self-learningUpon completion of this curriculum the modern approach of modelling and simulation to wastewater treatment plant design and operation, be it activated sludge, biological nitrogen and phosphorus removal, secondary settling tanks or biofilm systems, can be embraced with deeper insight, advanced knowledge and greater confidence.ISBN: 9781780401867 (eBook)ISBN: 9781843391883 (Print)

Coagulation and Flocculation in Water and Wastewater Treatment provides a comprehensive account of coagulation and flocculation techniques and technologies in a single volume covering theoretical principles to practical applications.Thoroughly revised and updated this new edition has been progressively modified and increased in scope to cater for the requirements of practitioners involved with water and wastewater treatment.New topics in this new edition include:activated sludge bulking and foaming control and enhanced bioflocculation;algae removal and harvesting;dissolved organic nitrogen (DON) removal;inorganics removal;turbidity and its measurement;wastewater treatment by coagulation and chemically enhanced primary treatment (CEPT).The book presents the subject logically and sequentially from theoretical principles to practical applications. Successive chapters deal with, in turn, properties of materials present in waters and wastewaters; characteristics and types of coagulants commonly in use; mechanisms and practical implications of destabilization of waterborne material using metal coagulants and polyelectrolytes; considerations and requirements for coagulant addition at the rapid mixing stage; theoretical and practical considerations of flocculation; and details of experimental procedures for assessing primary coagulants, flocculant aids, sludge conditioners, and flocculation parameters. Numerous examples are included as appropriate.Treatment and disposal of sludges resulting from coagulation-flocculation related operations is dealt with in an Appendix. This important topic has been separated from the main text to avoid disturbing the continuum of the presentation.Coagulation and Flocculation in Water and Wastewater Treatment is a readable and useful resource for the water scientist and engineer. It is a convenient reference handbook providing numerous examples and appended information and it is a vital text for course material for undergraduate and postgraduate students.ISBN: 9781780407500 (eBook)ISBN: 9781780407494 (Print)

Achieving basic water security, both harnessing the productive potential of water and limiting its destructive impact, has always been a societal priority. To capture this duality, water security is defined here as the availability of an acceptable quantity and quality of water for health, livelihoods, ecosystems and production, coupled with an acceptable level of water-related risks to people, environments and economies. This paper looks broadly at those countries that have achieved water security, the paths they chose and the costs they paid, and those countries that have not achieved water security and how this constrains economies and societies. It defines three typologies: countries that have harnessed hydrology, those hampered by hydrology and those that are hostage to hydrology. It finds that countries remaining hostage to hydrology are typically among the world's poorest. They face “difficult” hydrologies often characterized by high inter- and intra-annual rainfall and runoff variability, where the level of institutional and infrastructure investment needed is very high and the ability to invest is low. This paper seeks to capture the dynamics of achieving water security in a hypothetical water and growth “S-curve”, which illustrates how a minimum platform of investments in water institutions and infrastructure can produce a tipping point beyond which water makes an increasingly positive contribution to growth and how that tipping point will vary in different circumstances. As there are inevitable trade-offs, achieving water security is never without social and environmental costs; in some countries these are significant, often unforeseen and even unacceptable. This brief analysis suggests that the only historically demonstrated path to achieving water security at the national level has been through investment in an evolving balance of complementary institutions and infrastructure, but that lessons exist for following this basic path in more sustainable and balanced ways. Insights are provided for balancing and sequencing investments, adapting to changing values and priorities, and pushing down the social and environmental costs. The paper concludes that most water-insecure countries today face far greater challenges than those that achieved water security in the last century and are wealthy countries today. They face more difficult hydrologies and a greater understanding of and therefore greater responsibility for, the social and environment trade-offs inherent in water management. As the costs of poor countries not achieving water security, in terms of human suffering, sustained poverty, constrained growth and social unrest, would be very high, achieving water security is a challenge that must be recognized and must be met.

At least 325 water-associated outbreaks of parasitic protozoan disease have been reported. North American and European outbreaks accounted for 93% of all reports and nearly two-thirds of outbreaks occurred in North America. Over 30% of all outbreaks were documented from Europe, with the UK accounting for 24% of outbreaks, worldwide. Giardia duodenalis and Cryptosporidium parvum account for the majority of outbreaks (132; 40.6% and 165; 50.8%, respectively), Entamoeba histolytica and Cyclospora cayetanensis have been the aetiological agents in nine (2.8%) and six (1.8%) outbreaks, respectively, while Toxoplasma gondii and Isospora belli have been responsible for three outbreaks each (0.9%) and Blastocystis hominis for two outbreaks (0.6%). Balantidium coli, the microsporidia, Acanthamoeba and Naegleria fowleri were responsible for one outbreak, each (0.3%). Their presence in aquatic ecosystems makes it imperative to develop prevention strategies for water and food safety. Human incidence and prevalence-based studies provide baseline data against which risk factors associated with waterborne and foodborne transmission can be identified. Standardized methods are required to maximize public health surveillance, while reporting lessons learned from outbreaks will provide better insight into the public health impact of waterborne pathogenic protozoa.

The value chain (VC) system is a key way to address important sanitation technological and institutional gaps in production and service delivery and could constitute a natural platform for development actions and also serve as a market systems approach to improve access to safely-managed sanitation. It has been suggested that sanitation could boost local and national economies and global interconnections with a growing recognition that the private sector can play a bigger role in delivering the Sustainable Development Goal for sanitation, and help businesses understand value-added and product opportunities. This book proposes a pathway towards re-thinking the sanitation value chain (SVC) and suggests that it should cover all processes, activities and products of enterprises/actors in the sanitation supply chain that provide value-added services within each stage. Following the Regenerative Sanitation Principles, this book presents a new perspective to the SVC known as the 'integrated functional sanitation value chain' (IFSVC) to address operational functions within sanitation systems in combination with sanitation enterprises, operators and external actors that support the growth of the sanitation economy. The underlying premise of this book is that the IFSVC represents a new perspective that would have major social, environmental and economic implications for local, national, regional and global sanitation service delivery. It is hoped that researchers, business leaders, entrepreneurs, government officials and funders will find this book valuable, and be inspired and enabled to carry sanitation work forward in their own spheres of operation. The book gives several examples of encouraging developments, particularly in technical and business model innovation. It is our hope that this book will provide the stimulus for new learning and its application, particularly through cross-disciplinary and cross-sector partnerships that bring together all the skills and capabilities needed to deliver a fully effective IFSVC.ISBN: 9781789061833 (print)ISBN: 9781789061840 (eBook)ISBN: 9781789061857 (ePUB)

The increasing structural and physical scarcity of water across the globe calls for a deeper understanding of trans-boundary water conflicts. Conventional analysis tends to downplay the role that power asymmetry plays in creating and maintaining situations of water conflict that fall short of the violent form of war and to treat as unproblematic situations of cooperation occurring in an asymmetrical context. The conceptual Framework of Hydro-Hegemony presented herein attempts to give these two features – power and varying intensities of conflict – their respective place in the perennial and deeply political question: who gets how much water, how and why? Hydro-hegemony is hegemony at the river basin level, achieved through water resource control strategies such as resource capture, integration and containment. The strategies are executed through an array of tactics (e.g. coercion-pressure, treaties, knowledge construction, etc.) that are enabled by the exploitation of existing power asymmetries within a weak international institutional context. Political processes outside the water sector configure basin-wide hydro-political relations in a form ranging from the benefits derived from cooperation under hegemonic leadership to the inequitable aspects of domination. The outcome of the competition in terms of control over the resource is determined through the form of hydro-hegemony established, typically in favour of the most powerful actor. The Framework of Hydro-hegemony is applied to the Nile, Jordan and Tigris and Euphrates river basins, where it is found that current hydro-hegemonic configurations tend towards the dominative form.. There is evidence in each case of power asymmetries influencing an inequitable outcome – at the expense of lingering, low-intensity conflicts. It is proposed that the framework provides an analytical paradigm useful for examining the options of such powerful or hegemonized riparians and how they might move away from domination towards cooperation.

Understand the effects of climate change on urban water and wastewater utilities with this collection of international scientific papers. Case studies and practical planning, mitigating and adapting information provided on greenhouse gases, energy use, and water supply and quality issues.ISBN: 9781843393047 (Print)ISBN: 9781780401737 (eBook)

Even though ozone has been applied for a long time for disinfection and oxidation in water treatment, there is lack of critical information related to transformation of organic compounds. This has become more important in recent years, because there is considerable concern about the formation of potentially harmful degradation products as well as oxidation products from the reaction with the matrix components. In recent years, a wealth of information on the products that are formed has accumulated, and substantial progress in understanding mechanistic details of ozone reactions in aqueous solution has been made. Based on the latter, this may allow us to predict the products of as yet not studied systems and assist in evaluating toxic potentials in case certain classes are known to show such effects. Keeping this in mind, Chemistry of Ozone in Water and Wastewater Treatment: From Basic Principles to Applications discusses mechanistic details of ozone reactions as much as they are known to date and applies them to the large body of studies on micropollutant degradation (such as pharmaceuticals and endocrine disruptors) that is already available. Extensively quoting the literature and updating the available compilation of ozone rate constants gives the reader a text at hand on which his research can be based. Moreover, those that are responsible for planning or operation of ozonation steps in drinking water and wastewater treatment plants will find salient information in a compact form that otherwise is quite disperse.A critical compilation of rate constants for the various classes of compounds is given in each chapter, including all the recent publications. This is a very useful source of information for researchers and practitioners who need kinetic information on emerging contaminants. Furthermore, each chapter contains a large selection of examples of reaction mechanisms for the transformation of micropollutants such as pharmaceuticals, pesticides, fuel additives, solvents, taste and odor compounds, cyanotoxins.ISBN: 9781843393139 (Hardback)ISBN: 9781780400839 (eBook)

The suitability of Advanced Oxidation Processes (AOPs) for pollutant degradation was recognised in the early 1970s and much research and development work has been undertaken to commercialise some of these processes.AOPs have shown great potential in treating pollutants at both low and high concentrations and have found applications as diverse as ground water treatment, municipal wastewater sludge destruction and VOCs control.Advanced Oxidation Processes for Water and Wastewater Treatment is an overview of the advanced oxidation processes currently used or proposed for the remediation of water, wastewater, odours and sludge.The book contains two opening chapters which present introductions to advanced oxidation processes and a background to UV photolysis, seven chapters focusing on individual advanced oxidation processes and, finally, three chapters concentrating on selected applications of advanced oxidation processes.Advanced Oxidation Processes for Water and Wastewater Treatment will be invaluable to readers interested in water and wastewater treatment processes, including professionals and suppliers, as well as students and academics studying in this area.ISBN: 9781843390176 (Print)ISBN: 9781780403076 (eBook)

ABSTRACT Diagram showing the cultivation of the native D. dissociatus MT1 isolated from the Algerian Sahara for tertiary wastewater treatment. The process includes microalgal experimental setup, biomass production, and wastewater treatment, resulting in high removal of nutrient and COD. Inadequately treated municipal wastewater remains a major environmental challenge in Algeria due to the limited efficiency of conventional treatment systems in removing nutrients and organic matter. In this context, preliminary evaluation of microalgae-based wastewater treatment using the native microalga ‘Dactylococcus dissociatus MT1’, previously isolated from the Algerian Sahara, highlighting its potential as sustainable and locally alternative for advanced wastewater polishing. Experiments were conducted using sterilised media, including raw secondary wastewater, filtered secondary wastewater, and synthetic wastewater (SWW), with bold basal medium used as a control. D. dissociatus adapted well to all media, exhibiting specific growth rates between 0.44 and 0.71 d− and maximum biomass concentrations of 960–1,490 mg/L. Nutrient removal assays revealed high bioremediation performance across all media, with ammonium removal reaching 99% and nitrate removal efficiencies of 91–98%. Orthophosphate was eliminated in most media, except SWW, where removal reached 83%. In contrast, SWW exhibited the highest chemical oxygen demand (COD) reduction (100%), compared with 93–97% in real wastewaters. As pH remained below 9 and bacterial activity was excluded, reduction in nutrients and organic matter may have been associated with microalgal uptake. However, the contribution of other physicochemical removal cannot be completely excluded and warrants further investigations.

ABSTRACT Four-panel graphical abstract on phosphate dispersion in soils in Obio/Akpor, Niger Delta, Nigeria. Panel A shows septic tank contamination risk to groundwater borehole well with 98% of domestic water from groundwater. Panel B shows soil column transport studies for Sand, Silt, and Clay with Sand peak 6.12 mg/L at 2400s and Clay dispersion up to 10.95 cm2/s. Panel C shows phosphate retention barrier at 4.5 meters depth with adsorption from 0.0087 to 0.1579 mg/g. Panel D shows modeling equation Cpred = Csource x exp(-0.043D) x SFseason, seasonal factors Wet SF=1.0 and Dry SF=2.5, and minimum safe setback distances: Sand 5.0 m, Loam 4.0 m, Clay 3.0 m, with R-squared 0.997. Arrows show contaminant movement direction. Groundwater contamination from onsite sewage systems poses critical public health risks in the Niger Delta, where nearly 98% of domestic water is sourced from aquifers. This study quantifies phosphate transport in homogeneous soils through column experiments and develops a practical predictive tool for septic system siting. Sandy soils exhibited rapid phosphate breakthrough, while clay soils showed significant retardation but extreme dispersion variability. Critically, adsorption capacity increased with depth, identifying a natural retention barrier at 4.5 m that directly informs minimum vertical separation distances. A modified 1D transport model was calibrated and validated against experimental data, substantially outperforming existing models. The validated model yielded a simplified seasonally corrected equation requiring only depth and seasonal inputs; minimum vertical separation distances of 5.0 m for sandy, 4.0 m for loamy, and 3.0 m for clayey soils; and a seasonal correction factor of 2.5 for dry months when contamination risk is elevated. A low-cost field protocol using hand texturing achieved strong agreement with laboratory results. This study provides an empirically validated framework for evidence-based septic siting in Niger Delta tropical floodplain environments, enabling regulators to establish defensible setback distances without requiring advanced computational expertise.

ABSTRACT For practitioners, educators, and students who rely on Excel for hydrological data analysis, assessing the significance of a Pearson correlation often ends at the coefficient of determination obtained from a scatterplot trendline. The formal significance test is frequently omitted, as Excel provides no built-in, one-step procedure for this inference. This paper presents an integrated Excel workflow that addresses this gap. The workflow consolidates regression modeling and exact significance testing into a single, automated procedure using only native Excel functions. It employs the LINEST array function to simultaneously extract R2, the F-statistic, and residual degrees of freedom; the sign of the correlation is recovered from the regression slope. It then computes the exact critical correlation coefficient via Excel's F.INV.RT function using a derived conversion formula. Built-in diagnostic steps enable screening of the classical regression assumptions before applying the test. Validation against R at three significance levels (α = 0.01, 0.05, and 0.10) confirms accuracy. Illustrative cases – including a strong-correlation dataset and a borderline case showing how sample size affects the significance decision – demonstrate how the workflow supports the transition from subjective R2-based assessment into a streamlined, statistically rigorous procedure suitable for both practice and teaching.

ABSTRACT Flowchart of the calibration workflow, from plant data and ASM1/BSM1 modelling with 19 parameters, through PRCC screening to 13 and Sobol analysis to 8, to GA and PSO calibration and model validation. This paper presents a hierarchical ASM1 calibration framework applied to the Tlemcen municipal wastewater treatment plant, Algeria, under limited data conditions, using the Benchmark Simulation Model No. 1 (BSM1) implemented in MATLAB/Simulink. This study combines Partial Rank Correlation Coefficient (PRCC) screening under steady-state conditions and Sobol variance decomposition under dynamic conditions within a sequential sensitivity analysis framework, progressively reducing the parameter space from 19 to 8 influential parameters, prior to dynamic calibration using Genetic Algorithms (GA) and Particle Swarm Optimization (PSO), simultaneously optimizing five output variables: COD, TSS, BOD5, SNO and SNH. Based on 10 independent runs, PSO significantly outperformed GA in solution quality (mean J = 0.3150 ± 0.0001 vs 0.3167 ± 0.0009) and stability, confirmed by a Wilcoxon signed-rank test (p = 0.0020). The calibrated model showed good agreement with 2024 measured data (NRMSE <0.40, NMAE <0.41, TIC <0.22). Validation on an independent 2023 dataset confirmed temporal robustness (TIC <0.35). The proposed framework provides a practical decision support tool for aeration management and energy optimization, with potential extensions toward automatic control strategies and digital twin development for similar Algerian WWTPs operating under constrained monitoring conditions.

ABSTRACT An electrocoagulation (EC) emerging reactor with a rotating anode was constructed to study its effectiveness in removing turbidity and total hardness from samples of Lake water. The EC process was carried out under varying operational parameters, including rotation speed (SR), current density, inter-electrode distance, electrolysis duration (RT), and solution pH. The optimum operational parameters were set at 75 rpm, 6 mA cm−2, 20 min, pH 8, and 10 mm, respectively. The effect of the rotating anode was adopted as the central focus of analysis to examine the nature and extent of its impact on the obtained results. The results showed high removal efficiencies of 88.3% for turbidity and 65.8 for total hardness, as well as low energy consumption and reduced electrode usage, resulting in a total operating cost of 0.192 US$ m−3. Furthermore, the study showed that the artificial neural network (ANN) model can successfully predict removal efficiencies for turbidity and total hardness. The optimized ANN architecture achieved a low mean squared error (MSE, 0.000644) and a high correlation coefficient (R = 0.97992) during the network training stage. The results indicate that the ANN model successfully captured the nonlinear relationships between the operational parameters and treatment performance.

ABSTRACT Devastating environmental effects of relying too much on fossil fuels include air pollution, acid rain and global warming. One renewable energy source that is crucial for slowing climate change is hydropower. However, climate change affects its potential and makes hydropower generation unpredictable. The bootstrap aggregating machine learning approach is being used in this study to evaluate the hydropower potential in intermittent river basins. The performance of the Bootstrap Aggregating (BA) model was benchmarked against Random Forest and Gradient Boosting algorithms, demonstrating superior predictive stability with an average absolute error of 5.46%. A regional model was developed using future precipitation data unique to the Antalya basin (2025–2055) under the RCP 4.5 intermediate emission scenario. The findings demonstrate that the approach effectively estimated power duration curves and cease-to-flow points, with only minor discrepancies between the modeled and observed data. Quantitative analysis using Area Under the Curve (AUC) revealed a downward shift in future energy potential, particularly impacting mid-range generation capacities. The influence of climate change on hydropower potential, emphasizing its role as a renewable energy source amidst growing water scarcity and energy demands. Future research may incorporate deep learning techniques to enhance these models.

ABSTRACT Six-step graphical abstract illustrating the progression from spatial–seasonal water-quality monitoring to strategic management of the Bua River: Analytical progression from spatial–seasonal physicochemical monitoring and η²-based effect-size assessment to water-quality vulnerability profiling, SWOT–TOWS strategic synthesis and climate-resilient management of the Bua River within the Zambezi Basin. (1) Monitoring covers upstream (Mchinji), midstream (Dowa) and downstream (Ntchisi) locations across cold–windy, hot–dry and rainy–wet seasons. (2) Factorial generalised linear models (GLMs) quantify Site, Season and Site × Season effects using eta-squared (η²) effect sizes. (3) The resulting water-quality vulnerability profile distinguishes interaction-sensitive parameters, season-dominated parameters, spatial hotspots and comparatively resilient or vulnerable conditions. (4) SWOT categorises catchment strengths (ecological assets and relatively resilient conditions), weaknesses (observed physicochemical vulnerabilities and monitoring/management limitations), opportunities (restoration, improved monitoring, policy alignment and climate-smart management) and threats (catchment degradation, erosion, nutrient loading, land-use intensification and climate variability). (5) TOWS translates these factors into four strategic pathways: SO (protect and leverage existing strengths), WO (use opportunities to address vulnerabilities), ST (use ecological and institutional assets to reduce emerging threats) and WT (prioritise preventive interventions in vulnerable reaches and seasons). (6) The intended outcome is climate-resilient Bua River management within the Zambezi Basin. River-water quality in strongly seasonal catchments cannot be understood adequately from spatial averages alone because hydroclimatic conditions can alter both the magnitude and direction of longitudinal patterns due to interactions. We utilised physicochemical water quality data from across three different sections of Malawi's Bua River in three distinct hydroclimatic seasons. Aware of the existing interactions, physicochemical parameter-specific factorial GLMs, eta-squared (η2) effect sizes and standardised Site × Season profiles were used to distinguish spatial, seasonal and interaction-sensitive responses. Site× Season effects were largest for temperature (η2 = 0.676), oxygen saturation (η2 = 0.666), pH (η2 = 0.519), dissolved oxygen (η2 = 0.486) and chlorophyll-a (η2 = 0.417), whereas Season dominated turbidity (η2 = 0.818), TDS (η2 = 0.802), ammonium (η2 = 0.625), EC (η2 = 0.617) and soluble reactive phosphorus (η2 = 0.586). Moving from environmental diagnosis to strategic synthesis, an evidence-informed SWOT–TOWS framework translated these findings into management priorities centered on protecting comparatively resilient reaches, targeting season-sensitive hotspots, reducing sediment and nutrient connectivity, strengthening riparian and water-quality monitoring, and incorporating hydroclimatic variability into catchment planning. The approach provides an interaction-aware basis for climate-responsive freshwater management in the Bua and comparable seasonal river systems in the wider Zambezi River Basin.

ABSTRACT Rapid urbanization has emerged as a defining global trend of the 21st century, reshaping landscapes, ecosystems, and human societies. Among the most affected ecosystems are urban lakes, which, despite their relatively small size, provide critical ecological, social, and cultural services that support urban resilience and sustainability. This scoping review synthesizes existing literature to examine the retrospective impacts and future prospects of urbanization on urban lake ecosystems. Findings highlight that urban expansion, land-use change, and intensified human activities disrupt hydrological cycles, increase pollutant loads, and accelerate processes such as eutrophication, sedimentation, and contamination, thereby threatening ecological integrity and human well-being. Urban lakes, however, continue to play vital roles in climate regulation, flood control, biodiversity preservation, and the provision of recreational and cultural values. Despite growing recognition of these functions, research on urban lakes remains fragmented across disciplines, often focusing narrowly on water quality or urban planning dimensions. By mapping current knowledge and identifying key themes, this review underscores the need for interdisciplinary approaches to urban lake management and calls for integrative strategies that balance ecological protection with urban development. The insights generated aim to inform sustainable urban planning, policy design, and ecological stewardship in the context of accelerating urbanization.

ABSTRACT Night flow falls from 76.2 to 35.7 L/s over two contract cycles and rebounds at a measured 17.1 L/s per year between them. Performance-based contracts are increasingly promoted for water loss reduction in middle-income countries, yet empirical evaluations of contracts remunerated on the minimum night flow are largely absent from the peer-reviewed literature. This study evaluated a two-year performance-based leak detection and repair contract covering a 212 km network with 15,500 service connections in Ain Aouda, Morocco, using 39 validated measurement nights across 14 campaigns, a georeferenced register of 1,229 repaired leaks, matched-site pressure records, and fully observed cost records. The contractor reduced the minimum night flow from 76.2 to 45.7 L/s on schedule; leakage then rebounded to 55.6 L/s within six months, yielding a natural rate of rise of unreported leakage of 17.1 L/s per year, before a second campaign reduced night flow to 35.7 L/s (a 53% reduction). Night pressures at matched sites were stable or lower during the rebound, excluding a pressure artifact and making the estimate conservative. With a measured night-day factor of 19.0 hours, the economic intervention interval from observed costs is 3 to 8 months as a central estimate, against 19 practiced, and the incremental cost of active leakage control lies below the utility's full cost of water. Design recommendations are proposed for night-flow-indexed contracts.