Keywords

1 Introduction

Resource depletion is one of the major problems that dictate the transition towards production and development models based on environmentally friendly strategies. Among the promising approaches aiming towards the conservation of resources, circular economy is listed. Water, being indispensable for industrial processes, in fact for life itself, is included in the resources that are endangered by the advancing climate change. The implementation of strategies in the most aggravating sectors of human activity, aiming at the deceleration and reversal of these developments, is crucial. The building sector is a significant contributor to the consumption of water, representing at the same time an important field for improvements. Not surprisingly, water is taken into consideration in all of the methods for buildings’ sustainability assessment. Reviews of water-related parameters’ integration in such systems can be found in studies focusing solely on this issue (e.g., [1]) or addressing it in a broader context (e.g., [2]).

The existing building stock, created in the course of several decades and representing different priorities and philosophies, is a major actor in the built environment’s sustainability. Hence, the rating of existing buildings’ environmental performance is very important. In this work, well-known sustainability assessment methods (BREEAM, DGNB, LEED) for existing buildings in use are critically reviewed regarding the integration of factors associated with water into their assessment structure and philosophy. Aiming at a wider scope of analysis, the most recent internationally applicable versions of these methods, addressing both residential and non-residential buildings, are examined. In this context, parameters associated with water as a used resource are included in the study (i.e. water pollution, flood risk, hot water-energy wise, etc., are not addressed). Issues referring to the relevant criteria applied in each method (content, basis of calculations, section and level of the assessment structure into which they are included, etc.) are investigated and systematically presented. The main thematic areas examined are identified. This analysis is preceded by the presentation of basic features of the examined schemes (“structural” issues, assessment processes, ranking categories, etc.), so that a solid framework is formed for the water-specific elements to be presented. It is noted that, within the present and the following text, the terms “method”, “system” and “scheme” are used interchangeably; the same applies also for i) the terms “residential” and “domestic” buildings/uses, and ii) the terms “environmental performance assessment” and “sustainability assessment”. The presented information regarding the issues explored in this study is derived mainly from the examined systems’ technical manuals/guides. This work results in the presentation of the approach adopted by each scheme with regard to the examined issues and in the subsequent detection of similarities and differences among them.

2 Description of the Examined Methods’ Basic Characteristics

2.1 BREEAM In-use

BREEAM (Building Research Establishment’s Environmental Assessment Method) was initially published in 1990, being, therefore, the first system to be introduced for the assessment of built environment’s sustainability. Through years and a continuous development process under the responsibility of BRE (Building Research Establishment), the method has expanded to address a variety of building uses at various stages of their lifecycles, as well as built environment’s larger scales. Among the constantly evolving versions of the method, which apply for different evaluation objects and or in varying geographical areas, the ones referring to the buildings in use are listed. The first version addressing this stage of buildings’ lifecycles was introduced in 2009 [3].

In this work, the most recent, internationally applicable versions for the assessment of in-use residential and non-residential buildings’ environmental performance are examined ([4] and [5], respectively). Student accommodation, hotels, care homes and hostels are classified as non-domestic buildings. The structure and the evaluation process of those two schemes is similar. Specifically, the evaluation process in both cases is divided into two parts: i) asset performance (referring to the actual performance of the examined asset)-Part 1 and ii) management performance (addressing the management processes)-Part 2; Parts 1 and 2 can be employed independently and receive separate scores. In each one of the two Parts, a plethora of parameters are examined. Those parameters are organised into major environmental sections. In case of the asset’s performance evaluation Parts, in both schemes [4, 5], those sections are: i) “Health and Well-being”, ii) “Energy”, iii) “Transport”, iv) “Water”, v) “Resources”, vi) “Resilience”, vii) “Land Use and Ecology”, viii) “Pollution”. In the context of the management performance assessment Part, the aforementioned set of environmental sections, with “Transport” being excluded, is accompanied by an eighth one entitled “Management”. In all cases (both Parts, both schemes), an additional environmental section (“Exemplary”) exists. With the exception of the latter section, all the others include assessment issues. In the context of each one of the assessment issues, a specified number of credits is available. Those credits (or some of them) are awarded to the assessed object depending on its performance regarding the evaluation criteria accompanying each issue. The ratio of the awarded by the available credits for each major environmental section is multiplied by its relative weighting, and the sum of those products, along with the contribution from the “Exemplary” section, provide the building’s score (in [%]). This score determines the classification of the building into one of the ranking categories defined by the method (acceptable, pass, good, very good, excellent, outstanding). The available credits in the “Exemplary” section are awarded based on the achievement of exceptional performance in the context of specific issues, within which this possibility is provided. The assessment issues themselves (i.e. the level of the method’s structure where the evaluation occurs) are structured based on a question accompanied by a number (variable among the different cases) of answers, each one corresponding to the awarding of a part of the available credits in this issue. The selection of each answer presupposes the fulfillment of specific requirements and conditions [4, 5]. Another component of the assessment process is the fact that, for the achievement of any level of ranking/certification, some minimum standards must be met (apart from the final score itself). Very few of those standards are prerequisite for all rankings and only for Parts 2 of the assessments.

While the general assessment processes and structures in the two schemes (residential and non-residential uses) have the same spine, some differences between them regarding individual factors can be identified. For example, the relative weights of the same environmental sections differ not only between Part 1 and Part 2 within one scheme (which is expected), but also between the respective Parts of the two schemes. In all cases, the sum of the relative weights of the environmental sections, excluding the “Exemplary” section, equals 100%. Another central difference between the two schemes lies in the available credits’ number within each environmental section.

2.2 DGNB System for Buildings In Use

Developed by the DGNB (German Sustainable Building Council), the homonymous system for the built environment’s sustainability assessment emerged in 2008 [6]. Its first version addressed new buildings of specific uses. Currently, versions of the method for many building uses, referring to various stages of their life cycle, and also to the bigger-than-the-building scales of the built environment, are available. The first DGNB scheme for the assessment of the sustainability of buildings in use was launched in 2006. Its most recent version, published in 2020 [7] and having an international scope of application, is the one analysed in this study.

This scheme applies both for residential and non-residential building uses [7]. Three major topics are defined in the system: i) “Environmental Quality”, ii) “Economic Quality”, iii) “Sociocultural and Functional Quality”. Each topic contains three assessment criteria, each one of which is accompanied by its relative weighting that outlines the criterion’s contribution to the building’s total score. The relative weights of the assessment criteria comprised in each topic sum up to the relative weight of the topic itself (“Environmental Quality”: 40%, “Economic Quality”: 30%, “Sociocultural and Functional Quality”: 30%). The assessment takes place at the criteria level. The available in the context of each criterion points are awarded –all or some of them– depending on the performance of the building in relation to a set of indicators; each indicator is accompanied by a number of available evaluation points and a set of requirements/conditions, the fulfillment of which determines how many of the aforementioned points are achieved. Generally, in each criterion’s context, 100 evaluation points can be achieved. In some cases, it is possible for the building to “achieve” more than 100 evaluation points but only up to 100 can be credited; there are some criteria in the context of which bonus points are available (increasing the upper limit of the possible-to-be-awarded ones). The awarded evaluation points in each criterion and topic, in combination with the respective relative weightings, are the basis for the derivation of the building’s total score, which is expressed as a percentage and leads to the building’s classification into one of the four performance ranks (bronze, silver, gold, platinum). In the examined scheme there are no criteria with minimum, prerequisite for the assessment, requirements (“knock-out criteria” [7, p. 15]).

An important feature of the assessments conducted with the examined system is the employment of the “continuous improvement” approach [7] for five out of the totally nine assessment criteria included in the method’s structure. This approach essentially consists of four steps (plan-do-check-act) and employs an iterative process. In those criteria, the evaluation of the actual performance and of the management-specific aspects takes place separately (two parts), with the four steps process belonging to the management assessment part. The sum of the available evaluation points in those parts (performance & management) within each criterion that comprises them, equals the respective sum of a “typical” criterion; in all criteria including those two parts, bonus points are also available.

2.3 LEED Operations and Maintenance

LEED (Leadership in Energy and Environmental Design) was initially launched in 1998 by the U.S. Green Building Council, and quickly developed far beyond the scope and possibilities of its pilot version. Currently it represents a major part of the built environment’s sustainability assessment systems application worldwide. Having been continuously evolving to include more building types and uses, as well as neighborhoods and cities, it can currently be implemented for a wide variety of assessment items. The scheme for the evaluation of the environmental performance of existing buildings in use was released as early as in 2004 [8]. It has since been regularly revised along with the whole LEED method; currently, two versions are applicable (i.e. LEED for Operations and Maintenance v.4 [9] and LEED Operations and Maintenance v.4.1 [10]), with LEED v.5 being on the way. In this work, the most recent applicable version, revised in 2023 (beta version) [10], is examined. It addresses non-residential and residential buildings and provides the possibility for interiors- and existing buildings assessments. The present analysis focuses on the latter one.

The evaluation method in this scheme is structured on the basis of seven environmental categories, into which all the examined parameters are classified [10]: i) “Location and Transportation”, ii) “Sustainable Sites”, iii) “Water Efficiency”, iv) “Energy and Atmosphere”, v) “Materials and Resources”, vi) “Indoor Environmental Quality” and vii) “Innovation”. Each one of those sections includes criteria, which are of three types: i) criteria including conditions, the compliance with which is required (no points are obtained), ii) criteria, a number of the available points in the context of which is required to be achieved (and or some requirements must be met), and the rest of them may or may not be awarded, and iii) criteria without any mandatory items, with the available corresponding points being achieved by the building depending on the degree of fulfillment of the listed in those criteria conditions. The available points vary among the criteria, and, hence, among the environmental categories; their total number in the scheme is 100. The building’s performance is reflected in the sum of the obtained points. Based on this score, the building’s final ranking is derived (certified, silver, gold, platinum).

3 Water in the Examined Methods

3.1 General Considerations

As expected, the consumption and management of water as a resource represents an indispensable part of the assessments performed by the three examined methods. The related aspects are mainly classified in one major category/section of each system, with certain individual factors being included in the scheme’s other major section(s).

In the case of BREEAM In-use, the central environmental section for the analysis of the themes examined in this work is “Water”. Some individual factors regarding managerial processes are included in the “Management” environmental section; of course, they are relevant only for Part 2 of the assessment. The latter individual parameters are related to a) the existence of a user guide aiding the building occupants in applying efficient strategies with regard to, among others, water, b) the existence of improvement targets for various issues, including water, and c) the implementation of green lease agreements –applicable only for non-domestic buildings– promoting the consideration of more efficient practices. The relative weighting of “Water” environmental section is 9% and 8,5% for Parts 1 and 2, respectively, when residential buildings are concerned. The respective relative weights in the scheme addressing other building uses are 11% (Part 1) and 9% (Part 2). Parts 1 and 2 of “Water” section contain 10 (9 applicable for residential buildings) and 4 assessment issues, respectively.

In the case of DGNB System for Buildings In Use, the parameters associated with water use, efficiency and management are included, in their vast majority, in the “Water” assessment criterion, which belongs to the “Environmental Quality” topic. References to the reduction of water consumption can also be found in two criteria belonging to the “Economic Quality” topic. These cases regard mainly the operations cost (a closed water cycle offers bonus points) and the procurement and operations processes (incl. a guideline referring also to water use for cleaning). “Water” assessment criterion accounts for a share of 5% of the final score (its weighting represents the1/8 of “Environmental Quality” topic’s relative weight).

Finally, the environmental category “Water Efficiency” of the examined version of LEED is the one that includes most of the issues addressed in this study. Only the management of rainwater is examined within another environmental category (“Sustainable Sites”). “Water Efficiency” consists of only one criterion, the compliance with the “requirements” of which is a prerequisite for the assessment; the fulfillment of other conditions included in it leads to the obtainment of more points. Specifically, 15 points can be obtained through the evaluation of “Water Efficiency” (out of the total of 100 ones available in the scheme); the achievement of 6 of them is a prerequisite for the assessment.

The study of the examined assessment methods led to the observation that the majority of the assessed parameters that are related to the issues investigated in this work can be organized into four main thematic areas: i) monitoring, ii) total water consumption (including drinking water and other water resources), iii) measures for the optimization of use and the minimization of consumption of water, and iv) reuse of greywater, rainwater and other types of “reclaimed” water. These are the main axes of the following analysis of each method’s approach to the assessment of the building’s performance aspects related to water use, efficiency and management. Some points referring to the features of each evaluation method are further commented on.

3.2 BREEAM In-use

In Table 1, information regarding the assessment of the 4 main thematic areas in the structure and context of BREEAM In-use is presented (residential and non-residential buildings), based on the contents of the respective technical manuals [4, 5]. Data related to the integration of the relevant aspects’ assessment in the method’s structure is presented in the second column of this table; the third column includes information on the parameters that are actually evaluated. Table 1 has been formulated on the basis of the contents of “Water” section for both residential and non-residential buildings [4, 5]. The differences between these two schemes are not presented in detail in Table 1, which includes information that describe the assessment’s main components.

Table 1. Examination of water use, efficiency and management in BREEAM In-use (“Water” environmental section)
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Other parameters appearing in the context of “Water” environmental section (not included in Table 1) are the encouragement of reporting the collected data (via an assessment criterion in Part 2) and the adoption of strategies targeting refurbishments and maintenance schedules and processes that enhance water efficiency (again, via an assessment criterion in Part 2). As mentioned in Sect. 3.1, also some factors mainly related to management are examined in the homonymous environmental section.

An interesting observation lies in the detailed evaluation of water efficient equipment. The method does not just encourage such equipment items’ application in general terms and or reward the resulting water consumption reduction, but it evaluates the performance of each relative asset (toilets, showers, etc.). Indicatively, it is noted that in the case of non-residential buildings, the related criteria account for about 69% of the 38 available credits within the “Water Efficiency” environmental section (in the context of Part 1-asset performance).

3.3 DGNB System for Buildings In Use

Table 2, structured in the same way as Table 1, outlines basic elements of the assessment approach within the system’s “Water” assessment criterion, based on [7].

According to [7], the target for drinking water consumption can be set on the basis of the values calculated for water demand in the respective criterion in DGNB System for New Buildings. In this calculation several factors are considered (demand and waste by users, parameters related to rainwater, building use, etc.).

The step “check” of the continuous improvement process is not included in Table 2 in its entirety. It comprises an additional indicator related to the analysis of data acquired through the monitoring process; this indicator evaluates whether and how (quantitatively/qualitatively) the data is analysed, for further assessments to take place. This indicator is highlighted here (outside Table 2) as a distinct, well defined intermediate process within the continuous improvement concept.

Another issue that can be highlighted is the fact that the calculation of water exploitation index or baseline water stress indicator (country-specific), depending on whether the assessed building is situated in Europe or elsewhere, is awarded by the system. It can be said that those indices reflect, in general terms, water scarcity conditions. This approach indicates an effort towards the consideration of the actual conditions prevailing. Furthermore, the fact that the target value determination can be decided upon on a comparative basis (sets of similar/comparable buildings, consideration of innovative buildings) enhances the employed approach’s relativity component.

3.4 LEED Operations and Maintenance

Analogously to Tables 1–2, Table 3 is formulated for the examined version of LEED; the information listed in this table is based on the contents and the structure of “Water Efficiency” environmental category, as presented in [10].

The water performance score, which forms the basis for the examination of the total water use, is calculated considering data on the total annual consumption, the gross floor area, the occupancy and the operating hours; the daily consumption per occupant and per floor area are derived and used as inputs. The calculated score reflects the performance of the assessed building relatively to the one of “comparable high-performing buildings” [10, p. 29], i.e. relativity-based considerations are explicitly referred to.

Table 2. Examination of water use, efficiency and management in DGNB Buildings In Use (“Water” assessment criterion)
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Measures for performance optimization or consumption minimization are not evaluated as autonomous units (e.g., examination of the equipment’s water efficiency or assessment of the implementation of such measures); of course, a better performance due to solutions of this kind is assessed via the consideration of the total water consumption. It is indicated in [10] that a series of relevant criteria in [9] list strategies that can be applied as potential improvement solutions. These strategies include water efficient - performing over specific baselines– equipment (fittings & fixtures), the reduction of water used for irrigation, issues related to water use metering, etc.

Finally, it is noted that the reference to rainwater within the environmental category “Sustainable Sites” addresses its management (e.g., practices of low impact aiming at the partial reuse of the rainwater falling on the site, related systems’ maintenance).

Table 3. Examination of water use, efficiency and management in LEED Operations and Maintenance v.4.1 (“Water Efficiency” environmental category)
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4 Conclusions

The preceding analysis highlighted strong similarities and differences among the three examined methods with regard to their basic features and the assessment philosophy that they employ, as well as to the way water-related parameters (efficiency, consumption, management) are assessed and implemented in their context (metrics/indicators/criteria used, relevant weights of the relevant sections, etc.).

Indicatively, the strong performance-based component is listed among the main similarities. Indeed, the monitoring of the actual water use/consumption is a central consideration in all three schemes, with features of this process (type and abilities of metering devices/ monitoring means, etc.) being explicitly specified. These characteristics, as well as other issues (e.g., whether the related requirements are mandatory or not for the assessment to proceed) vary to different degrees among the examined methods. Another similarity lies in the fact that the calculation and assessment of the actual total water consumption is shared as a concept. However, the way of points’ obtainment (assessment basis) is not of a uniform philosophy. For example, the relativity element (i.e. consideration of buildings similar/comparable and or technically innovative) is explicitly inherent in the assessment process, partly or structurally, of some of the examined methods. In all cases, the use of recycled/reclaimed water (rainwater, graywater, blackwater, etc.) is strongly acknowledged and rewarded, again via varying routes. The same applies for the water use reduction measures, which are addressed in several ways: assessed as autonomous items (equipment’s efficiency evaluation), integrated in a holistic approach to performance improvement, or referred to as possible improvement strategies, they are an essential part of the analysis. Another important similarity of general nature among the three methods is the strong consideration of management processes, which are either a structural part of the analysed criteria assessment, or additional requirements described in other sections of the scheme.