Assessment of Peak Water Usage among Residential Consumers across Several Drinking Water Service Areas

By inergency On Feb 14, 2024

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1. Introduction

Issues that have attracted worldwide attention and research, particularly since 2000, are access to drinking water for human consumption, its responsible use and its growing scarcity, primarily due to factors such as water stress resulting from human activities and events related to climate change [1]. The severity of these challenges has prompted organisations such as the United Nations (UN) to focus their efforts on defining the Millennium Development Goals as well as measuring progress and compiling data on a global scale. Two sustainable development goals (SDGs) in particular have gained prominence: SDG 6, which aims to “Ensure availability and sustainable management of water and sanitation for all” [2] and SDG 11, which aims to “Make cities and human settlements inclusive, safe, resilient and sustainable” [3].

The concern expressed by governments towards safeguarding and responsibly using resources and their fair access is shown in the Millennium Development Goals (MDGs), which require the implementation of adaptive strategies by several stakeholders, including governmental bodies, private institutions, non-governmental organisations and end-users [1]. The absence of localised or regional policies concerning the public usage of drinking water, which incorporate an understanding of supply system vulnerabilities and a clear assignment of responsibilities among societal actors, is a significant barrier towards advancing adaptation efforts. Consequently, against a potential shortage and deterioration of water resources, both related to the quantity and quality of surface water [2], the inclusion of demand control measures, such as rational water consumption patterns, efficient distribution systems within urban areas and low-consumption or water-saving devices within building internal networks, within this policy have been proposed to ensure the sustainable usage of water resources.

In developed nations such as Australia and the United States (which historically show the highest daily water consumption per person), a decline in user water consumption has been observed, supported by the implementation of conservation strategies and the use of low-consumption or water-saving devices and sanitary fixtures [4]. The efficacy of these measures hinges on sociodemographic variables [5,6,7] and alterations in behaviour linked to the preservation of water resources [8]. These behavioural changes are influenced by a paradigm shift in the cultural perception of water (water stewardship), changes in societal water usage patterns, adoption of water-saving or low-consumption technological systems and cultural norms surrounding water use, all of which are interconnected with climate change [9]. This collective effort serves to alleviate strain on lotic ecosystems and, in turn, safeguard water resources.

Within certain Latin American nations, efforts to alleviate pressure on water resources have centred around programmes aimed at managing water demand, which also include projects geared towards promoting the rational use of water and the integration of water-saving devices in new constructions [10]. Nevertheless, several studies and official data within the region reveal a notable dichotomy in relation to this matter. In this regard, through assessments aimed at comprehending the scope of the water problem, the UN Human Settlements Programme highlights daily per capita water consumption statistics that vary significatively depending on local regulations, as well as the explanation of usual daily peaks of the consumption. Regarding the United Kingdom, the average daily water consumption stands at 121 litres per household [11]. Additional regional studies indicate that in two Campina Grande districts in Brazil, factors such as service fees and family income play a role in influencing water consumption patterns. In the first scenario, it was observed that when service rates increase, consumption also increases. However, in the second scenario, there is some research on the GDP rise when consumption decreases [12]. In Sonora, Mexico, other factors directly affecting water consumption have been identified. These include population growth, heightened population density, the expansion of alternative water sources (such as groundwater), significant levels of technical and commercial losses and the substitution of high-water-consumption equipment with more water-efficient alternatives [13]. The Madrid region also uses high-tech innovative approaches to achieve more efficient water management, i.e., smart water consumption monitoring systems. The water and sanitation sector in Chile has achieved full cost recovery and implemented universal micro-metering and progressive monitoring of consumption volumes. This, coupled with the investments in network maintenance, the stabilisation of unaccounted water control and the consolidation of water and sanitation service providers under a few major groups, has resulted in cost synergies and economies of scale. Despite these achievements, the benefits have not been transferred to consumers in the form of lower rates [14].

In Colombia, the delivery of drinking water is governed by a range of laws, in particular Law 142 of 1994, which establishes the foundation for public utility services. This legislation is the legal framework that delegates responsibilities to government bodies and encourages healthy competition among private service providers at a national level. Further, Law 373 of 1997 mandated utility companies to present programmes or plans for the efficient use and conservation of water. Subsequently, the national policy for the Integrated Water Resource Management was introduced (2009), with the intention of addressing the underlying issues contributing to inadequate government oversight in terms of resource regulation and control. This policy aimed to harmonise the efforts of governmental institutions. Moreover, it revealed a problem indicative of inefficient water usage among users, service providers and decision makers. This scenario implied a challenge in the search for the sustainable management of water resources [15]. In its pursuit of effective and comprehensive water resource management, particularly in relation to aqueduct service providers, the Colombian Government sanctioned Resolution CRA 750 of 2016 through the Regulatory Commission for Drinking Water and Basic Sanitation. This resolution modified the range of basic consumption and defined complementary and luxury consumptions, aiming to contribute to efficient water use and discourage irrational consumption. Within this resolution, the range of basic potable water consumption per user and per month was revised from 20 to 17 m³ in cold climate cities (18 m³ in temperate climates and 19 m³ in warm climates). Furthermore, the same CRA resolution laid a gradual reduction plan for basic water consumption in cities such as Bogotá, targeting a decrease of 11 m³ per month in 2018 [16].

At the local level, in 2012, the Mayor’s Office of Bogotá took steps to ensure the provision of free water (recognised as a fundamental right) for individuals in a manifest state of vulnerability, a move aligned with the Colombian constitutional jurisprudence at both the local and national levels. This was enacted through Executive Order 064 of 2012, which granted 6 m³ of free water to residential users in Strata 1 and 2 in Bogotá (per user, where a user has an average of 5.5 inhabitants in stratum 1 and 4.9 inhabitants in stratum 2, which are the object of coverage of this policy), aiming to enable dignified living conditions as provided in the Political Constitution [17]. In this context, in the first year of implementation, the supply of the vital minimum amount of water in the city produced figures where households in Strata 1 and 2 in Bogotá (~626,602 benefiting users or subscribers) consumed an average of 0.53 m³ more water per month compared to the previous year [18].

As part of the strategy to regulate water consumption among users beyond the rate aspect, the Colombian Institute of Technical Standards (ICONTEC) implemented the Colombian Technical Standard NTC 1500 [19], based on the International Plumbing Code, for designing internal water and wastewater networks in buildings. This standard establishes the minimum requirements for internal networks within buildings under a rational and efficient approach to water usage through the regulation and definition of criteria governing network design, construction, installation, operation and maintenance, including material quality and the integration of water-saving devices to minimise overall consumption volume and subsequently reduce the peak consumption rates within buildings. Additionally, this standard is referenced and managed by the Bogotá Aqueduct and Sewerage Company (EAAB) in their technical standard for internal networks, NS-128, which also highlights the need for new installations to incorporate sanitary devices bearing environmental labels that indicate appliances and equipment with low water consumption [19,20]. The focus of the primary analysis conducted in this study revolves around the efforts geared towards optimising consumption.

When a building, whether residential, commercial, institutional or industrial, incorporates multiple sanitary fixtures (such as showers, sinks, basins, toilets, washing machines, hose taps and bathtubs), each fixture inherently requires a specific minimum instantaneous flow value linked to the discharge flow rate for which it was designed (a value that essentially corresponds to the average discharge flow rate of a typical fixture). The maximum instantaneous flow rate, also known as the maximum possible flow rate, is the sum of the instantaneous flows caused by each of the sanitary fixtures operating simultaneously. Nevertheless, the actual consumption within the building is lower than the outcome of this calculation as the simultaneous operation of all fixtures under normal circumstances is rare. It is not easy to determine, in a general sense, how many fixtures will be used simultaneously at any given moment due to the construction aspects of the fixtures and their faucets. Above all, this variability arises from their intermittent use, with varying frequencies depending on the types of buildings and where they are located, the hygienic habits of their users and other socioeconomic factors. Nevertheless, different methodologies are used to prudently estimate a simultaneity factor. The probable maximum flow rate of a building denotes the anticipated flow rate within the system, factoring in the aforementioned simultaneity of use [21].

The Colombian regulation governing the design of internal hydraulic and sanitary installations in buildings, “NTC 1500”, suggests determining the anticipated maximum flow rate within a building (used as the design flow rate for sizing internal networks) through the use of the probabilistic methodology called the Hunter curve. This methodology stems from a probabilistic approach introduced by Roy Hunter that is based on studies or measurements conducted on buildings in the United States. However, this methodology may not necessarily align perfectly with the conditions, characteristics and consumption patterns of the Colombian population, particularly within the city of Bogotá. This was confirmed by recent studies, which confirmed that the design flow rates calculated using this approach notably differ from actual consumption rates observed in these buildings [22]. These discoveries, along with research conducted by professionals specialised in the design of internal networks in buildings, have supported the enhancement of the curves and data that currently function as design benchmarks within the standard above [23].

Considering the extensive water service infrastructure in the city of Bogotá and its more than 2.2 million users as of 2022, along with the various initiatives undertaken by the EAAB in alignment with the requirements of Resolution 750 of 2016 by CRA and Decree 064 of 2012 from the Mayor’s Office aimed at ensuring an optimal and efficient water supply under parameters of rational consumption and effective resource use between 2009 and 2011, the EAAB conducted a field measurement campaign of specific flow rates in residential areas involving 1233 users located across different service areas within the city. Additionally, a survey system was implemented to characterise residential users, understand their composition and identify types of water-using fixtures and purposes. Based on field measurements and surveys, a research project was conducted to use and analyse the information collected by the EAAB to study and determine various aspects, including the characteristics and behaviour of residential consumers. This was achieved by calculating the per capita average daily consumption of registered users and measuring the real-time maximum flow rates as instantaneous pulses in each building studied. These measurements were then compared with the probable maximum flow rates previously established during the design of internal networks in buildings using standardised methodologies used globally, including the one recommended by NTC 1500 for Colombia. This analysis serves as the foundation to determine which methodology is more appropriate for the specific conditions of how residential users in Bogotá consume water in terms of peak flow rates.

The significance, distinctiveness and innovative perspective of this study centres around its capacity to analyse a sample of 1233 residential users representing diverse socioeconomic backgrounds. Moreover, this study involves utilising field measurement equipment to determine the actual maximum flow rate that passes through a building’s inlet pipe over an observation period of ~20 days; then, these measured datasets are compared with the methodology commonly used in Colombia for calculating the probable maximum flow rate for designing internal networks as well as with other alternative methods used at regional and international levels. This topic is relatively underexplored in Colombia and Latin America and provides a contrasting perspective against the methodology proposed in the National Regulations issued by ICONTEC. The results from this study offer decision-making tools for designers, service providers and even governmental bodies such as the Colombian Vice-Ministry of Water and Sanitation that are aimed at implementing similar studies and regulations based on real field measurements. These measurements serve as inputs for selecting or designing a reliable and precise methodology for sizing and designing water supply systems in residential buildings, ensuring efficiency and compliance with current regulations to achieve the following objectives:

A streamlined design: This is achieved by precisely calculating instantaneous peak flows, which are essential for designing efficient internal water distribution systems that fulfil users’ needs without wasting resources.
Proper network sizing and dimensions: This helps in understanding that the actual instantaneous flow is critical for correctly sizing pipes, valves, pumps and other components within the internal network to prevent issues related to over- or under-sizing.
Water preservation: This enables precise calculations of consumption volumes based on real user consumption data, which enables the identification of opportunities to incorporate water-saving technologies like low-flush devices or dual-flush toilets, contributing to the preservation of water resources.
Supply security and quality by service providers: This indicates that knowledge of peak flows is pertinent for ensuring adequate water availability during periods of high demand, such as peak hours or emergencies. Moreover, it directly impacts the safety and comfort of building occupants and enables service providers to design external hydraulic networks that cater to these needs.
Compliance with regulations: This is required for comparing and evaluating various methods to determine the most appropriate method for residential buildings in Bogotá. This process also aids in identifying approaches that align best with local regulations and guidelines and ensure adherence to the specific standards set by authorities.
A platform for replicating similar projects in the local and regional context, targeting other user categories: This allows service providers, the government and universities to contribute towards new projects aimed at determining peak consumption behaviour and the most fitting calculation method for each city or region. This approach accommodates method evolution based on current fixture conditions and user behaviour.

The focus of this research is to evaluate and understand user demand patterns, particularly during peak hours, to inform the design and management of both distribution networks and interior building networks within the context of public drinking water services. This involves assessing various methods for estimating probable maximum flow rates and their impact on network sizing, with a focus on residential consumers in Bogotá, Colombia.

3. Results

Based on the readings captured by the Aquabus Y290 micro-meter, and keeping in mind that the equipment records the peak flow rate that enters the building at a given instant of time within the 20-day time window in which it was installed, the statistical values of this recorded peak flow of each user, in order to determine with the sample data the maximum peak flow, minimum peak flow, arithmetic mean and median of the peak flow rates—which are the basic statistics of central tendency indicators—for each service delivery area. These findings are detailed in Table 5, offering an analytical perspective on the flow data collected from users within each area, specifically those concerning the recorded instantaneous peak flow rate at the point of entry into the residential network.

At the maximum peak flow level in all service provision sectors (A2 to A5), the maximum peak value recorded corresponds to the upper end of the meter reading, which reflects that within the sample some users were characterised as consuming water outside the normal range of a residential user.

Across the assessed zones, the measured probable maximum peak flow rate was 1.82 L/s for all 1233 residential users studied. (At the maximum peak flow level in all service provision sectors (A2 to A5), the maximum peak value recorded corresponds to the upper end of the meter reading, which reflects that within the sample some users were characterised as consuming water by outside the normal range of a residential user. However, from the visual analysis of Figure 6, it is observed that the maximum peak flow rate within the operating range of the equipment is approximately 1.4–1.6 L/s). The A2 area had the highest measured minimum flow rate at 0.12 L/s, whereas areas A3 and A4 showed the lowest extreme value at 0.06 L/s. The average flow rate across all areas varied between 0.45 and 0.50 L/s, whereas the medians ranged from 0.37 to 0.42 L/s. These values served as the data for comparing the flow rates obtained by each of the probable maximum flow rate calculation methods analysed in the study. For each area and method, a scatter plot of measured vs. projected flow rates was created, as shown in the example below for area 3. Figure A1, Figure A2 and Figure A3 present the results for the remaining areas.

Based on the scatter plot analysis comparing measured and calculated flow rates, as depicted in Figure 6, we can see that the majority of the calculated flow rates are above the average flow rate line. In contrast, a substantial portion of the measured flow rates lie below this threshold. There is a noticeable differentiation in the distribution of these flow rates, indicating a significant dispersion between the calculated and measured data. In addition, for each area, the calculated average flow rate line is depicted, which reveals, for each method, the proximity between the average lines of measured and calculated flow rates as well as the method that yields a probable instantaneous maximum flow rate result that is closest to the measured reality of users.

Below, the authors provide a summary of the average results obtained through several methodologies for calculating probable instantaneous maximum flow rates. These methodologies were applied to residential users in areas 2 to 5, which correspond to the water service provided by the EAAB in Bogotá. These results are compared with the average flow rates obtained from measurements conducted for users in areas 2–5.

Table 6 shows the average values of the calculated probable instantaneous maximum flow rates using the nine different methods evaluated in this study. These methods are used worldwide for designing internal building networks.

Here, only one empirical method—the British method—was used for the population studied. This method is the second-most overestimating of the maximum instantaneous flow rate calculated in comparison to the measured flow rates. In general terms, it triples the actual expected flow rate.

Among the semi-empirical methods studied and fully applied (four methods), the rational method yielded the best results when compared to the measured maximum flow rates. Due to its close resemblance to the measured actual flow rates and the fact that it has slightly increased flow rates even when they are similar, the rational method emerges as one of the recommended methods for designing internal building networks in Bogotá. On the contrary, the method producing the furthest calculated probable instantaneous maximum flow rate from the measured rate is the German square root method, which overestimates the expected real flow rate by 3–4 times.

Of the four studied and applied probabilistic methods, it was determined that the original Hunter method calculated much higher flow rates than the measured ones, nearly doubling them. Although the Chilean RIDDA regulation method and the Hunter NTC 1500 method generate lower flow rates than the Hunter method, they still produce flow rates substantially higher than the measured ones (by ~60%). Finally, the Hunter Unal method, proposed by the National University of Colombia, best aligns with the water consumption patterns specific to the population of Bogotá. This method achieves the results of probable instantaneous maximum flow rates that are closest to the measured maximum flow rates for the studied users. However, when applying this method to a highly representative sample size of 1233 residential users, out of the total sample, the method generates slightly higher flow rates than those measured for ~55% of the population; for the remaining 45%, the calculated flow rates are slightly lower than those measured. This could potentially lead to the design of internal networks that are undersized during simultaneous peak consumption events in relation to the actual flow needs, especially in multi-family buildings such as apartment complexes, which are increasingly common due to rapid demographic growth and limited available space for accommodation. Therefore, it is crucial to persist in studying, calibrating and validating this calculation methodology using both present and future flow rate data. The objective is to enhance the accuracy of the Hunter Unal method by extending the scope of the research study to include other cities with diverse climatic conditions and cultural practices as well as other institutional (schools and government and private offices), commercial (large and small business establishments) and industrial buildings. In these scenarios, specific calculation methods for probable instantaneous maximum flow rates must be developed according to the distinctive characteristics of each use type.

In relation to the results of the average instantaneous maximum flows determined by different methods and the measured flows in each area, we can see that, even when each method determines a flow rate in relation to different calculation criteria, they showed consistent and uniform results when compared across areas. This suggests that even though user behaviour, practices and consumption patterns show considerable diversity, there is a coherent and measurable behavioural trend that can be characterised and quantified.

Figure 7 shows the average probable instantaneous maximum flow rate results obtained using the nine methods across the four study areas. Figure 7 also includes the average measured flow rates for each area, allowing for a graphical observation of the previous conclusions regarding the accuracy of each method and the uniformity and consistency of the results when assessing each method independently across the four areas.

Bear in mind that in Europe, the EN 806-3 [25] was developed by the CEN (European Committee for Standardization); it is a simplified method and is only applicable to small installations. However, countries such as Germany (DIN 1988-300) [26] or Portugal generally consider other methods. Discussions about the methodologies implemented in Europe have been taking place for many years [27].

4. Sizing Case Study

To compare the results of the estimated probable maximum flow rate obtained from the nine methods assessed against the measured flow rate, as well as to illustrate how the use of the probable maximum flow rate affects the sizing and design of an entry pipe for a building considering the actual internal diameter of PVC pressure pipes for internal networks, the following paragraphs discuss sizing for one of the users assessed. This analysis will be conducted assuming an entry speed of 1.50 m/s, which is the typical design speed used in internal networks to ensure self-cleaning and minimise transient effects (the speed recommended by NTC 1500 falls between 1 m/s and a maximum of 2.5 m/s).

For the calculation, the real internal diameters of PVC pipes are used. Table 7 presents the analysed pipes.

For the example above, we used data from a user located in area 5 (a house, Stratum 3, located at CL 40F SUR 78A 10). This allowed us to demonstrate the estimation results of the probable maximum flow rate and the sizing of the entry pipe. The arrangement of the hydraulic fixture points in the building is detailed in Table 8.

For the case study, by considering the measured flow rate, applying the nine methods for calculating the probable maximum flow rate and assuming an average water speed through the pipe of 1.5 m/s as well as an expected range of actual speeds between 1 and 2 m/s, we used the continuity equation to determine the probable maximum flow rates of the user selected for the case study. We also calculated the theoretical and actual diameters that would be used in the entry pipe to the building based on the internal building network design approach. In addition, leveraging the PVC pipe pressure database, we determined the price per linear metre of the pipe defined for the probable maximum flow rate of each method. Finally, we calculated the percentage of additional cost that each method incurs when compared to the design created for the conditions of the measured actual flow rate. The results are detailed in Table 9.

The results clearly show that the required diameter for the entry section of the internal network of the building, considering the measured flow rate, would be 0.75″. Only the rational and Hunter Unal methods yield the same diameter, whereas the other methods report diameters between 1″ and 1.5″. The factors of probable maximum flow rate increase relative to the measured rate, varying from a minimum of 0.98 for the Hunter Unal method to 1.28 for the rational method. However, for the other methods, this factor ranges from 1.72 to 4, with the maximum factor obtained using the German square root method. The cost analysis of the designed pipes demonstrates that the projected additional cost on site, solely due to the pipe supply, ranges from 140% to 330%. These results underscore the significance of appropriately selecting a probable maximum flow rate calculation method that not only optimises hydraulic sizing but also minimises the economic expenses linked to constructing internal networks.

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