The first step in this work was to study the current literature and models related to the assessment of water consumption in the residential sector. This step was crucial as it gives insights into the methods and strategies used in the assessment of water consumption. Moreover, it defines the water-saving factors and variables which have the highest influence on residents to lower their water consumption. The literature study revealed that water consumption in the residential sector is strongly influenced by water tariffs, level of water awareness, level of water behavior, and technology use in residents’ homes. Hence, these variables were adopted in this study as input for the Fuzzy model. On the other hand, the output of the Fuzzy model was chosen as the water-saving index (WSI), defined as the ratio between the daily water consumption per capita in Abu Dhabi, and the daily world-average water consumption. Hence, if the water-saving index is less than one, this means that the water consumption per capita in a specific country is less than the world’s average water consumption, and vice versa. According to the Environment Agency-Abu Dhabi (EAD, 2016), the water consumption of Abu Dhabi Emirate per capita is almost 3 times the world average, which means that the value of the current WSI can be used as 3.
In order to prepare the Fuzzy-logic model, both input and output variables need to be fuzzified. Fuzzification is a process in which a certain crisp variable is converted into fuzzy. This is primarily possible if one can establish that the variable under consideration is not deterministic and carries a considerable amount of uncertainty due to imprecision, ambiguity, or vagueness (Ross, 2017, Alhamad and Saraiji 2022). Then, the variable can be represented using an appropriately designed membership function which can characterize the vagueness, or most accurately, the fuzziness of the variable. Membership functions were first introduced by Zadeh (1965) in his first research paper “Fuzzy Sets”. The fuzzification process includes two major aspects; the first one is to find the best membership function that describes the variable based on the current literature and the second aspect is to represent this membership function with the proper linguistic terms. Hence, pre-defined variables such as water tariffs (input) and water-saving index (output) can be easily fuzzified based on the current state of both of them. For example, the current water tariffs ($2 per cubic meter) can be said to be “medium or current tariffs”, or have a 100% membership degree in the medium or current subset. Anything lower than the current water tariffs can be part of the “low tariffs” membership function subset and anything higher can be part of the “high tariffs” subset. Values between 1 and 2 are having different degrees of membership in both the low and medium subsets, consequently, values between 2 and 3 have different degrees of membership in both medium and high subsets. The same applies to the water-saving index, where the current value of 3 can be said to be “current WSI”, while anything lower or higher can be said to be “low WSI” and “high WSI” respectively. The membership functions of water tariffs (WT) and water-saving index (WSI) are shown in Fig. 1 and Fig. 2 respectively.
However, the fuzzification of the rest of the input variables (level of water awareness, level of water behavior, and level of technology use) is not straightforward. Data related to the level of each one of these variables in Abu Dhabi households are needed. Although several studies have been done to measure the people’s overview of different water-saving policies in Abu Dhabi Emirate (Alhamad, 2018 a), the water usage patterns of Abu Dhabi residents (Yagoub et al., 2019), water demand forecasting (Kizhisseri et al., 2021; Mohamed et al., 2020; Younis, 2016), and the environmental awareness of Abu Dhabi youth (MOEW, 2014), the need for recent robust data was required. Moreover, it is believed that measuring the level of water influences through their direct indicators gives more reliable and consistent data. For example, measuring the level of technology use through actual indicators such as the respondent’s adoption of water-efficient appliances or water recycling activities is more accurate than asking opinion questions related to the effect of water technologies in saving water.
Hence, in order to fuzzify the input variables of water awareness, water behavior, and technology use, a survey was designed and distributed amongst a sample of students and employees of United Arab Emirates University (UAEU) in Al Ain-Abu Dhabi. The output of the survey will be used as a baseline for the fuzzification of these input variables. The survey comprises a total of 32 questions. The initial 10 questions gather personal information such as age, gender, place of residence within the Abu Dhabi Emirate, education level, etc. The remaining questions are formulated either as Yes or No inquiries or as 5-point Likert scale questions, where respondents choose the answer that best describes their opinion or behavior, or indicate their level of agreement/disagreement with a given statement on a scale of 1 to 5. On this scale, 1 represents complete disagreement, while 5 signifies complete agreement. The survey participants were selected to include individuals who are residents of the Abu Dhabi Emirate only. No additional survey sampling was required. A total of 91 responses were collected. The statistical analysis of the data was conducted using IBM SPSS Statistics. Table 1 shows a summary of the descriptive statistics of the respondents’ traits collected at the beginning of the survey.
A tailored set of questions were designed to measure the level of awareness, positive water behavior, and technology usage through their direct indicators, and then a combined variable for each set of these questions (components) was developed (based on the median of components) to represent the level of awareness (WA), water behavior (WB), and technology use (TU). For this purpose, it was assumed that the Likert scale items data are continuous variables rather than ordinal variables. Although this assumption may not be very accurate compared to other analysis methods such as factor analysis. However, it is justified in many cases to avoid the complexity and sophistication of factor analysis methods (Robitzsch, 2020). Moreover, the idea behind the survey was not to develop generalized results about the respondents but rather to provide clear insights needed for designing the membership functions (fuzzification of variables). Table 2, Table 3, and Table 4 show the descriptive analysis for the combined variables "level of water awareness", “level of water behavior”, and “level of technology use” respectively, along with their individual components, and Fig. 3, Fig. 4, and Fig. 5 shows the frequency charts of the same variables.
Table 1
Summary of descriptive statistics for the survey respondents’ traits
Variable | Categories | Frequency (No.) | Percentage (%) |
Age | Less than 18 | 12 | 13.2 |
18–24 | 61 | 67 |
25–40 | 9 | 9.9 |
More than 40 | 9 | 9.9 |
Total | 91 | 100 |
Gender | Male | 39 | 42.9 |
Female | 52 | 57.1 |
Total | 91 | 100 |
Location within Abu Dhabi Emirate | Abu Dhabi city | 11 | 12.1 |
Al Ain city | 59 | 64.8 |
Al Gharbiah | 2 | 2.2 |
Other | 19 | 20.9 |
Total | 91 | 100 |
Housing Status | Owner | 65 | 71.4 |
Tenant | 26 | 28.6 |
Total | 91 | 100 |
Educational level | Secondary school | 2 | 2.2 |
High school | 36 | 39.6 |
Bachelor | 48 | 52.7 |
Higher education | 5 | 5.5 |
Total | 91 | 100 |
Number of family members | 1–2 | 3 | 3.3 |
3–5 | 18 | 19.8 |
6–8 | 32 | 35.2 |
More than 9 | 38 | 41.8 |
Total | 91 | 100 |
Number of toilets in the household | 1 | 3 | 3.3 |
2 | 5 | 5.5 |
3 | 10 | 11 |
4 | 8 | 8.8 |
5 and more | 61 | 67 |
Total | 91 | 100 |
Availability of water services such as swimming pools and fountains | Yes | 36 | 39.6 |
No | 55 | 60.4 |
Total | 91 | 100 |
Availability of landscape irrigation services | Yes | 66 | 72.5 |
No | 25 | 27.5 |
Total | 91 | 100 |
Table 2
Descriptive analysis for the combined variable "Level of Water awareness". and its components
| WA-1 | WA-2 | WA-3 | Level of water awareness (WA) |
Responses | 90 | 90 | 90 | - |
Mean | 2.69 | 3.64 | 3.31 | 3.33 |
Median | 3.00 | 4.00 | 3.00 | 3.00 |
Mode | 2 | 5 | 3 | 3.00 |
Std. Deviation | 1.34 | 1.33 | 1.06 | 1.07 |
Variance | 1.81 | 1.78 | 1.138 | 1.14 |
WA-1: I periodically read the water bill and study its details WA-2: The impact of public awareness on water consumption is effective WA-3: How do you rate the water consumption in UAE compared to the average global consumption? |
Table 3
Descriptive analysis for the combined variable "Level of Water behavior". and its components
| WB-1 | WB-2 | WB-3 | Level of water behavior (WB) |
Responses | 90 | 90 | 90 | - |
Mean | 4.13 | 4.41 | 3.43 | 4.20 |
Median | 5.00 | 5.00 | 3.00 | 5.00 |
Mode | 5 | 5 | 5 | 5.00 |
Std. Deviation | 1.265 | 1.048 | 1.391 | 1.20 |
Variance | 1.600 | 1.099 | 1.934 | 1.44 |
WB-1: I turn off the tap while brushing my teeth WB-2: I make sure that the water taps are turned off before I leave the house WB-3: I carry out periodic maintenance on taps and water pipes to ensure that they are free of any leakage |
Table 4
Descriptive analysis for the combined variable "Level of Technology use". and its components
| TU-1 | TU-2 | TU-3 | Level of technology use (TU) |
Responses | 90 | 90 | 90 | - |
Mean | 3.62 | 4.02 | 2.69 | 3.6778 |
Median | 4.00 | 4.00 | 3.00 | 4.0000 |
Mode | 5 | 5 | 1 | 3.00 |
Std. Deviation | 1.259 | 1.122 | 1.346 | 1.13006 |
Variance | 1.586 | 1.258 | 1.812 | 1.277 |
TU-1: On an individual level, I don't mind paying an extra amount to install/purchase new technologies that save water TU-2: Do you think that the use of modern methods at the domestic level for water retreatment, such as (residential graywater systems) contributes to saving water? TU-3: Do you reuse water at home, such as: water from air conditioners for agriculture or water for fishponds...etc. ? |
To begin the fuzzification process, the frequency charts derived from the histogram of the combined variables were carefully examined. These charts provided valuable insights into the distribution of data points and directed the determination of linguistic terms associated with different levels of the variables. Hence, it was utilized to guide the fuzzification process.
Linguistic terms such as 'low', 'medium', or 'high' were assigned to represent different levels of water awareness, water behavior, and technology use according to the observed frequency distribution. Linguistic terms were assigned to different ranges or bins based on the observed frequency distribution in the histogram. By analyzing the shape of the histogram, including peaks, valleys, and clusters, appropriate linguistic terms were determined to represent various levels of the variables. For instance, the frequency distribution of the combined variable for water awareness (Fig. 3) revealed a concentration of data points around the value of 3 and dropping beyond this value, hence, this point was assigned the linguistic term “medium”, which refers to the current state of water awareness of Abu Dhabi residents and reflected on the membership function which has a scale from 0 to 100% as 60%. Anything below that value was assigned a linguistic term of ‘Low’, with variable degrees of being “Low” and “medium” in the range from 40–60%, and anything above this value was assigned a linguistic term of ‘High’, with variable degrees of being “medium” and “High” from 60–80%. The shape and parameters of the membership functions were established considering the observed frequency distribution, expert knowledge, and domain understanding. The membership function of the level of water awareness is shown in Fig. 6.
A similar approach was used for the technology use as the frequency distribution of the combined variable for technology use (Fig. 5) revealed a concentration of data points around the value of 3.5 and continued to be almost of the same level of frequency values as the end of the scale, hence, this point was assigned a linguistic term of ‘High’, which refers to the current state of technology use of Abu Dhabi residents and reflected on the membership function which has a scale from 0 to 100% as 70%. Values below 70% were assigned linguistic terms of ‘low’ and ‘medium’ with different degrees of each subset based on the histogram distribution. The membership function of the level of technology use is shown in Fig. 7.
For the water behavior membership function, the frequency distribution of the combined variable for the water behavior (Fig. 4) showed that the concentration of data points is around the maximum value of 5, which indicates a high level of water behavior among Abu Dhabi residents. Hence, this point was selected to be the “high” subset. However, the values of frequency of data points between 3 and 4 are almost constant, hence, they were selected to be the “medium” subset, and this was also reflected in the membership function of the water behavior by making the “medium” subset to be constant between 60% and 80% after converting to a scale of 0 to 100%. Values below 40% were selected to be on the ‘Low’ Subset with different degrees of being “low” in the range of 40–60%. The membership function of the level of water behavior is shown in Fig. 8.
Following the fuzzification process, the subsequent step involves the application of fuzzy logic rules or inference mechanisms to assess the influence of each variable on the water-saving index. This step enables the evaluation of the fuzzy relationships between the input variables (water tariffs, level of water awareness, level of water behavior, and level of technology use) and the water-saving index. Fuzzy logic rules are formulated to capture expert knowledge or domain understanding regarding the impact of the input variables on the output variable (water-saving index). These rules typically take the form of "if-then" statements, specifying the relationships between linguistic terms or fuzzy sets of the input and output variables. For instance, an illustrative fuzzy logic rule could be expressed as follows:
"If the water tariffs are high and the level of water awareness is high and the level of water behavior is high and the level of technology use is high then the water-saving index is low"
The process of generating or extracting fuzzy rules, which serve as a pivotal tool for mapping input variables to the output variable, does not have a standardized methodology. Rather, it heavily relies on the expertise and knowledge of the individual responsible for establishing the fuzzy logic model (Bai and Wang, 2006). Hence, these rules are derived through a combination of expert knowledge and the literature on the topic under consideration. The number of rules needed for the fuzzy logic model to fully describe the simulated system corresponds to the total number of potential scenarios that may arise as a result of the arrangement of the input membership function subsets (Alhamad and Saraiji, 2022). The proposed model has 4 input variables with 3 subsets each. Hence, the number of needed rules is equal to 81 rules.
Once the fuzzy logic rules are established, the subsequent stage involves conducting fuzzy inference. Fuzzy inference integrates the linguistic terms or fuzzy sets of the input variables, utilizing the defined rules to determine the corresponding fuzzy set or linguistic term for the water-saving index. Various inference mechanisms can be employed, such as Mamdani (1980) which was used in this study, or Sugeno (1985), depending on the specific requirements and characteristics of the study. The output of the inference process is a fuzzy set or linguistic term representing the overall impact or degree of influence of the input variables on the water-saving index. To obtain a crisp output or a numerical value for the water-saving index, a defuzzification process is typically applied. Defuzzification methods, such as centroid or max membership, are utilized to convert the fuzzy set into a crisp value that can be interpreted and compared. The methodology used in this work can be summarized in Fig. 9.