This paper proposes a system of energy performance indicators for the comprehensive assessment of water distribution networks, framed within urban water infrastructure governance, where energy efficiency is a critical element for sustainable service provision. The framework combines global efficiency metrics with a detailed characterisation of specific energy losses, enabling a structured and transparent evaluation of how energy is consumed and dissipated in pressurised networks. The proposed indicators quantify energy consumption relative to the supplied volume and allocate losses to friction, leakage, excess pressure and pumping station inefficiencies. Ideal reference values and achievable target scenarios are incorporated to contextualise observed performance, enabling the identification of efficiency gaps and the definition of realistic improvement margins that can inform planning and regulatory processes. Indicators such as manageable topographic energy and the Energy Efficiency Index (EEI) provide decision-support tools to assess efficiency levels and the effectiveness of management measures. The methodology supports energy audits, prioritisation of interventions and evidence-based planning, promoting sustainable and resilient water supply services under increasing energy and climate pressures.

This paper describes energy diagnostics for water networks, which are complex systems with one or several inputs and multiple outputs, and also describes the ENERGOS tool created to perform the diagnostics. This tool was designed and conceived to be easy to use and mainly requires few data from the system. For target setting, ENERGOS has a set of wizards that guide the user in setting these limits and proposes values based on experience, the literature or regulations.

ABSTRACT In improving the energy efficiency of water transport systems, two critical stages are involved: assessment (to understand the system's operation and identify potential energy savings) and auditing (to locate and break down the energy losses). Both stages are based on energy balances, which can be conducted using either the extended Bernoulli equation or the energy integral equation. Both equations can be applied, but depending on the system, data availability, and the kind of study to be performed, one is preferable over the other. This paper analyses, applies and compares both equations, with a particular focus on the less commonly used energy integral equation in the hydraulic field. This more general equation includes thermal and transient effects and it is more suitable for analyzing complex systems. In contrast, the extended Bernoulli equation, while simpler to apply, can lead to the loss of relevant information, such as the evaluation of the topographic energy. The main objective of this work is to bridge the gap between these two fundamental energy equations and recommend the most appropriate one for hydraulic problems. Real examples are presented to show their differences and validate our recommendations.

El presente trabajo analiza el comportamiento energético de los sistemas de transporte de agua a presión simples, en los que una tubería trasiega agua desde el punto origen hasta el final. El objetivo del análisis es evaluar la eficiencia energética del sistema y, a partir de ella, formular una propuesta de certificación energética. Para ello, se calculan tres valores representativos del indicador intensidad energética Ie, (kWh/m3): la intensidad energética ideal Iei; la Intensidad energética real Ier, cociente entre la energía realmente consumida (kWh) y el volumen trasegado (m3) en idéntico periodo de tiempo, y, por último, la Intensidad energética objetivo, Ieo, valor de la energía unitaria suponiendo un funcionamiento real óptimo. El resultado del cociente Ier/Ieo sintetiza el margen de mejora del sistema y, por tanto, es el utilizado para calificar su eficiencia energética. El trabajo concluye con un ejemplo real que reproduce el procedimiento establecido.

This paper establishes the minimum amount of energy required by a simple system, a benchmark established on the basis of current technology and the requirements by energy regulators, weighting costs, and efficiency. The first step is to normalize the energy intensity (kWh/m3), which is the quotient between the energy consumed and the volume pumped, with the geometric gradient. The new normalized parameter is more objective than the commonly standardized one with the pumping head due to its dependence on friction. In addition, it makes it possible to naturally disaggregate energy needs (in useful and dissipated energy during transport) to establish a target energy intensity and evaluate existing savings. The quotient between energy intensities (actual and target) allows qualifying transport efficiency. At the same time, it permits extending the policy of energy labeling to pressurized water transport, which has been proven to be a successful energy efficiency strategy.

This paper analyses the energy performance of simple pressurised water transport systems, in which a pipe transfers water from the point of origin to the end. The aim of the analysis is to evaluate the energy efficiency of the system and, on this basis, to formulate a proposal for energy certification. To do this, three representative values of the energy intensity indicator Ie, (kWh/m3) are calculated: the ideal energy intensity Iei; the real energy intensity Ier, the quotient between the energy actually consumed (kWh) and the volume transferred (m3) in the same period of time; and, finally, the target energy intensity, Ieo, the unit energy value assuming optimal real operation. The result of the Ier/Ieo quotient summarises the margin for improvement of the system and is therefore used to qualify its energy efficiency. The work concludes with a real example that reproduces the established procedure.

Pressurized water transport has a highly energy consumption and must be reduced to mitigate Climate Change impacts. This energy reduction can be achieved by optimizing the process: reducing the volume of water to be transported (managing water demand and reducing water losses), and adjusting pressure with an eco-layout. This work compares the traditional water distribution design (the objective of the current method, prevailing for more than one century, is to minimize the investment and to guarantee the supply), with an eco-layout, whose objective is to prioritize efficiency, adjusting the pressure as much as possible to the service needs. This is an alternative and logic approach in a new framework: Safer electrical networks, reliable electromechanics' equipment and the imperative need to reduce energy consumption. The eco-layout is more convenient from an environmental point of view and, besides, it is more economic, if all expenses are considered.

Although the transport of fluids by pipeline is the most efficient, it requires high energy consumption, due to the volume transferred and the pressure required. This is the consequence of transporting large volumes of water (sometimes over considerable distances) and having to deliver it at the required pressure. In the current context of climate change, with both resources becoming increasingly scarce, the only way to minimize their impact and control energy consumption is to improve efficiency, a process whose most relevant stages are the diagnosis, which identifies the starting point and the existing margin for savings, and the audit, which locates and quantifies inefficiencies. This paper presents a simple tool, ENERGOS, which allows to perform the first stage, the energy diagnosis of a pressurized water system. The objective of this diagnosis is to know the current state of the system, and more importantly, the possible margin for improvement, if any, from the introduction of very few data. This is the first step to improve the efficiency of the system. The tool, and the energy indicators presented in it, have been designed under the premise that only the minimum information, which any manager should know about his system, is required. That is, global volumes billed and injected, the most representative system levels and energy consumed by the pumps (available in the electricity bills). ENERGOS classifies the systems into three large groups, and performs the diagnosis according to the group. These are, firstly, the simple systems, defined as a pipeline, with one entry, generally, one pump, and one exit. Multi-scenario systems are systems with several inputs and outputs, and constant changes in their mode of operation, where each of these scenarios corresponds to a different layout. Finally, networks with one or more inputs and numerous outputs can operate differently, but without changing the layout. In all cases, the tool has a schematic, simple and intuitive data entry part, and from the data entered, it calculates the diagnosis, consisting of the comparison of the current energy intensity indicator (kWh/m3) with the ideal energy intensity, the one that would imply the total absence of losses, both operational (friction, water losses, inefficiencies in the pumping stations) and structural (losses due to topography). Since it is impossible to reach the ideal energy intensity value, an intermediate indicator, the target intensity, is defined. The calculation of this intensity requires the establishment of targets for losses, reasonable reference values to be achieved with the current technology for the system under analysis. For example, the current efficiency of the pumping station is estimated, and a minimum acceptable level is calculated for it (establishing values for the efficiency of the motor, the variator and the pump itself). The same is established for friction, water losses and excess pressure.

Aligned with the goals of achieving higher sustainability in water systems, the minimization of energy costs is a top priority for the operators and owners of such systems. Early research contributions on the rate of energy dissipation due to head losses, defined as energy slope J, demonstrated that this parameter can be optimized so that such cost minimization is achieved. However, an important factor that was not considered in previous research is that water demand might be variable during the lifetime of water systems. Whether due to daily variation patterns, seasonal changes, or long-term water demand growth, variations on the flow rate complicates the determination of the optimized energy slope J(opt) , that will minimize energy costs. This work addresses this knowledge gap, performing an evaluation of how demand variation impacts J(opt) and how deviations from the optimum energy slope affect costs for varying water demands. In addition, this work also provided insights into pipe cost installation terms and pipe cost exponents using real-world data of existing water systems in Spain. Such exponents are very important in the computation of optimum energy slopes. It is hoped that this research will provide practical guidance to designers and operators of water systems regarding the minimization of energy costs, leading to greater sustainability of such systems. (C) 2022 American Society of Civil Engineers.

Esta obra es fruto de la traducción al español del libro de Indicadores de desempeño para servicios de abastecimiento de agua de la International Water Association.Se trata del segundo libro de una serie de tres traducciones de manuales de buenas prácticas de la IWA que están viendo la luz gracias al compromiso del grupo Global Omnium con la mejora de la gestión de los servicios urbanos de agua. El manual que tiene ante sí es ya todo un clásico que fue actualizado hace apenas un año y medio en su versión inglesa. Se trata sin duda de la referencia en todo el mundo para desarrollar sistemas de evaluación del desempeño con el uso de indicadores, hasta el punto que resulta prácticamente imposible encontrar un artículo o trabajo sobre este asunto que no referencie esta obra. Por ello, debe tomarse como un punto de partida más que uno de llegada. El manual proporcionará los fundamentos de la evaluación del desempeño y las claves para acometer la misma con éxito en un servicio de abastecimiento de agua. Para los más experimentados, este manual siempre será una obra de referencia a la que volver cuando surjan dudas.

Energy intensity, Ie (kWh/m3) is the most popular indicator when characterizing the energy requirements of the water cycle, due to its direct and easy interpretation. In pressurized water transport systems, when referred to an appropriate physical framework (such as a single water transport pipeline), it assesses the efficiency of the process. However, in complex urban water transport networks, Ie only provides a basic notion of the energy needs of the system. The aim of this paper is to define a standard physical framework for assessing the energy intensity in water transport and distribution systems. To that purpose, an analytic expression that estimates Ie is proposed, based on system data and its operating conditions. The results allow for a realistic approximation of the energy needs of water transport. This energy assessment is completed with two context indicators: energy origin (C1) and topographic energy (θt), both essential when the energy efficiency of different systems is to be compared.

Frontier efficiency methods have been recurrently used in the water sector to assess the performance of water utilities. These methods are also used for yardstick regulation, with greater efficiency being sought by creating competition between the utilities, which can have an impact on decision-making processes, such as tariff setting. This study analyzes the adequacy and limitations of these methods for regulatory purposes, particularly how they deal with data uncertainty and their capacity to manage large number of variables. In order to achieve this, two representative methods—a nonparametric technique (data envelopment analysis) and an econometric one (stochastic frontier analysis)—are applied to an audited sample of 194 water utilities. Results will show that the results from the methods may not be considered conclusive in the water sector and their application should be carried out with considerable reservations.

Water infrastructures are rapidly ageing without being properly replaced. Communicating the state of the network and the sector's needs to stakeholders is key for guaranteeing the sustainability of water and sewage systems. The infrastructure value index (IVI) is becoming a standard in the water industry as a communication tool; however, as a single value metric, it can mask key information. The complementary use of the infrastructure degradation index (IDI) and the infrastructure histogram (H-i) can provide a better understanding of the network's state while maintaining the simplicity of the analysis needed for public dissemination. The IVI is focused on the value of the infrastructure, the IDI on its median remaining life. The H-I provides a detailed but simple picture of the network's remaining life, providing a clear idea of the magnitude of the investments needed in the future for maintaining the infrastructure.

Pressurised water transport systems are highly energy-intensive. Therefore, in the context of resource scarcity and climate change, efficiency is essential. To achieve this, it is necessary to (1) assess the state of the process and (2) evaluate the existing margin for potential improvement. These are the two objectives of this work, which is based on the energy intensity Ie (kW h m−3) of a process that can simultaneously be expressed in units of pressure. Considering water transport, and its incompressible behaviour, there exists a biunivocal relationship between Ie and the sum of energy required to transport water, which can be expressed as equivalent height H (m, energy per unit of mass). From the energy intensity (Ie) and energy requirements (H), the efficiency of a water transport system in operation is evaluated. From installations in the design phase, the range of Ie values that are needed to achieve efficiency can be predicted. The proposed procedure is general, simple and precise, as demonstrated through three case studies.

To achieve maximum efficiency in water pressurized transport, it is necessary to perform a global analysis, whenever possible starting from the system's conception. The first stage of the process is the network layout, the main topic of this paper. The optimum topology from an energy point of view (or eco-layout) is the one that, insofar as is feasible, allows equalizing the network's pressure to the set pressure standards. Eco-layouts can be easily designed in new systems but are difficult to implement, mainly in the short term, in operating networks. Nevertheless, because no system is eternal, the required actions can be gradually implemented. Therefore, the main goal of this paper is to identify and discuss these guidelines and actions, some of which are apparently contradictory to current design criteria, whereas others endorse modern management trends. These strategies can be summarized in two points: (1)providing lower pressure to consumers saves energy, and (2)setting up smaller pressure zones in terms of the elevation steps between zones will enable water companies to supply water at lower pressure in hilly areas. In the end, networks with more-efficient layouts can achieve important energy savings. (C) 2018 American Society of Civil Engineers.

A significant amount of energy is required to operate pressurised water distribution systems, and therefore, improving their efficiency is crucial. Traditionally, more emphasis has been placed on operational losses (pumping inefficiencies, excess leakage or friction in pipes) than on structural (or topographic) losses, which arise because of the irregular (unchangeable) terrain on which the system is located and the network's layout. Hence, modifying the network to adopt an ecologically friendly layout is the only way to reduce structural losses. With the aim of improving the management of water distribution systems and optimising their energy use, this work audits and classifies water networks' structural losses (derived from topographic energy), which constitutes the main novelty of this paper. Energy can be recovered with PATs (pumps as turbines) or removed through PRVs (pressure reducing valves). The proposed hydraulic analysis clarifies how that energy is used and identifies the most suitable strategy for improving efficiency as locating the most suitable place to install PRVs or PATs. Two examples are discussed to illustrate the relevance of this analysis.

Se repasa, en el marco del contexto mundial, la evolución de la desalación en España. Una historia de más de medio siglo que arrancó donde el agua más escasea, en las Islas Canarias. Lo que comenzó siendo una solución puntual para resolver problemas concretos ha ido, al compás de los avances tecnológicos, de la reducción de costes y del control de su impacto, ganando relevancia. Pero hace quince años, el ritmo de implantación, se aceleró notablemente. En aquel contexto se tomaron rápidas decisiones, adoptadas sin el amplio consenso que requieren este tipo de infraestructuras. Sin embargo, la madurez tecnológica y, sobre todo, el tiempo están contribuyendo a clarificar la situación, propiciando que cada desaladora encuentre su lugar y, en fin, justificando la fuerte inversión efectuada. Con todo hay problemas aún pendientes de solución, en particular la incorporación de esta nueva fuente de agua en un sistema que integre todos los recursos, tanto los tradicionales como los nuevos. Ello exige que los usuarios acepten su sobrecoste como un nuevo seguro hídrico que permita garantizar el suministro de agua en todo momento. En cualquier caso, hay que concluir que la desalación en España juega, y continuará jugando un papel clave en el litoral mediterráneo y en algunas de sus islas más turísticas.

A summary of the evolution of desalination in Spain, spanning over half a century of history, follows. What started as a solution to resolve occasional water shortages in islands where natural surface and ground water resources were scarce, has gained more relevance with technological advancements, less expensive production costs and at the same time minimizing the impact on the environment. But fifteen years ago, the normal pace of history underwent an about-turn with the sudden construction of a significant number of desalination plants. The speed, and on occasions the haste, involved in many of the decisions, brought about some imbalance between the different players that were involved. Time, and above all, technological advancement have clarified the situation, and most of the desalination plants that were built have managed to find their place, thus justifying the investment that was made. But there are still some stages to address, particularly that of integrating these plants in the joint water resource operation systems. In this regard, consumers must accept that desalination plants competing with traditional water resources, greatly improve the guarantee of supply, and in fact act as a new water insurance that, indeed, has a cost. Today however, and particularly in the future, desalination in Spain plays and will continue to play an essential role, especially in the southeast Mediterranean region and in some of the more touristic islands. The following is a brief history.

In this paper, an algebraic expression is presented to determine the optimum hydraulic gradient (J(0)) in a pressurized water system. J(0) represents the economic level of friction losses (ELF), which is dependent on the network's behavior as well as other parameters, including energy and the pipe costs. As these have prices changed over time, so has the value of J(0). The network-related parameter was obtained from the total costs function and the sum of the operational and capital expenditures. Because these costs exhibited an opposite trend from J, a minimum total cost exists, specifically, J(0). The algebraic expression, which was derived from the mathematical model of the network, was first calculated for the network's steady state flow and was later generalized for application to a dynamic one. For a network operating in a given context, J(0) was fairly stable in terms of dynamic flow variations, providing valuable information. The first piece of information was the ELF itself, which indicated the energy efficiency of the system from the perspective of friction loss. The second indicated which pipes required renewal from a similar perspective. Thirdly, it provided a simple criterion to calculate the diameter of new pipes. Finally, as J(0) can be easily updated, when predictions are performed at the network's designed time fail (e.g., growing urban trends, demand evolution, etc.), decisions can also be updated.

The discussed article proposes a new resilience index based on the required nodal pressure 7 necessary to reach the standard minimum pressure in the whole system. This interesting 8 reflection leads to this discussion, with three objectives. 1) to emphasize the need to unify 9 terminology and working hypotheses in any energy analysis, 2) to revise the concept of 10 resilience within the framework of climate change