Keywords

1 Introduction

The water crisis has many effects on the future sustainability, especially sustainable urbanism. Water scarcity affects four out of ten people around the world, and it's projected that by 2050 about 3.9 billion of the world’s population will live in water-stressed river basins (Guppy and Anderson 2017). For each degree of global warming, approximately7% of the global population will be exposed to a decrease of renewable water resources of at least 20% (Döll et al. 2015). Furthermore; urbanization is increasing in many megacities and leads to huge water demand which is increasingly difficult to supply, this is exemplified by the recently avoided Day Zero event in Cape Town (2018) and the water crisis in Chennai, India. Despite that; water infrastructure systems are deteriorated in many countries, for example, 30% of the global water abstraction is lost through leakage and about 80% of wastewater flows back into the ecosystem without being treated (Guppy and Anderson 2017). Worldwide, domestic sector consumes about 10% of the total water consumption, although households are the smallest consumer of water, but it has an enormous potential impact and water use in this sector is expected to go upward by 80% over the next 25 years (Danielsson 2019). Water shortage in many world countries is considered to be one of the most challenging constraints of achieving sustainability in social housing projects. This is even more acute in developing countries, especially megacities where there is a mismatch between population and housing supply (Nasr et al. 2017).

As a way of codifying sustainability in buildings, certain measures are incorporated in the form of green building rating systems. Green certified buildings saved an average of 37.6% compared with the baseline water usage rate for all buildings (Cheng and Peng 2016). Leadership in Energy and Environmental Design (LEED) rating system; developed by the United States Green Building Council; is the most common rating system around the world. LEED rating system consists of six main categories: sustainable site planning, energy efficiency, indoor environmental quality, materials and water efficiency (USGBC 2014). The water efficiency credits in LEED v4 focus on reducing indoor and outdoor water consumption in buildings, requiring prerequisite baseline achievement for each. The main indoor water use reduction method is to upgrade baseline appliances to more water efficient products. Outdoor water reduction methods include limiting the amount of irrigated landscape, switching to water efficient plant species, using alternative water resources, and completely eliminating an irrigation system (Greer et al. 2019).

To make buildings water efficient, the Reduce, Replace and Reuse approaches should be adopted. Under the Reduce approach, buildings should have a monitoring system, employ water efficient products and design a leak-free system; in addition, there should be Replacement for the use of potable water with seawater or rainwater for non-potable uses. Finally, there should be a Reuse mechanism like the implementation of a graywater system (Marinoski et al. 2018). To solve the water problem, it is necessary to consider the water supply services. Furthermore, the design of the built environment, the open spaces and the water infrastructures, integrating between gray and green infrastructures is important to achieve sustainable development (Tahvonena and Airaksinenb 2018).

The research aim is to study the water efficiency in social housing projects and to measure the efficiency of using the available water conservation strategies; taking into consideration the special circumstances of each project. The gap in currently existing literature is represented in rarely considering the assessment of water efficiency in social housing projects; in addition to not addressing the combination between all the available water efficient strategies and how they could be integrated.

2 Methodology

The paper is adopting an analytical comparison study between two social housing projects in Cairo and São-Paulo; as two megacities facing water challenges; the comparison is considering the water efficient requirement in sustainable housing projects. The two case studies were selected in two countries with convergence in the economic and social situations; in addition to the variations in the experiences of each country. The first case study in Cairo is New-Cairo social housing project, which is located in New-Cairo district, which is considered as an urban extension for Cairo city; the project is selected as it represents a typical example for most of the social housing projects in Egypt. The second case study in São-Paulo is Paraisópolis social housing complex, which is located in Paraisópolis slum; the project is selected as it represents a sample of social housing projects in Brazil and it followed some water efficiency regulations. The two projects have some variances in the locations, urban context and design; and this will help in providing more detailed observations on water efficiency related to the different aspects of each project. The research followed some steps to evaluate the water situation in the two projects; first is studying the water problems affecting the sustainability of water resources in each country in order to analyze the predicted future challenges. Second is the water efficiency assessment for the two case studies through the field studies, surveys and questionnaires. Third is studying the available opportunities for improving water efficiency; to show how some water efficient strategies could be integrated in the design in order to improve water efficiency and achieve sustainability. Finally, comparing the results of the two projects to show how environmental, social and economic conditions aspects affected the water consumption and efficiency in each project.

3 Case Study 1—New-Cairo Social Housing Project in Cairo, Egypt

Egypt is 96% dependent on Nile River as the major source of water supply. This water is bounded by international treaties and so the quota of Egypt, which represents 55.5 billion m3/year; may be affected by many variables such as the Ethiopian Renaissance dam, which may cause the Nile’s fresh water flow to Egypt to be cut down by 25%. Egypt is located in arid climate, the annual average of rainfall is 12 mm and ranges from 0 mm/year in the desert to 200 mm/year in the north coastal region. In Cairo the average rainfall is 25 mm/year. In Egypt today, 104 billion m3 of water are required to cover the country water needs. Renewable water, coming from the Nile River, rain and underground water, only reached 62 billion m3. Egypt currently covers its shortage of water through reuse of agricultural drainage water which reached 20 billion m3. Meanwhile, Egypt suffers from a shortage of 42 billion m3. Egypt now is under the poverty water line with 600 m3/capita/year and is predicted to be 350 m3/capita by 2050, while the water poverty line is 1000 m3/capita/year. The overall country average/capita usage of drinking water is about 300 L/day. The amount of drinking water produced in the year 2017 was about 9.3 billion m3 and the loss rate of it reached 29.7% due to the leakage. The case study is located in New-Cairo district, which is east of Cairo. The average annual temperature is 20.8 °C in New-Cairo and about 28 mm of precipitation falls annually. The stormwater system and infrastructure in New-Cairo isn't qualified to hold extreme rain events as flash floods and inundations occur in many areas each year during specific storms (Gado and El-gha 2019).

3.1 Water Efficiency Assessment of New-Cairo Social Housing Project

The project was carried out through two phases, the research focuses on the second phase shown in Fig. 2.1 which is more recent, and began operation in 2016; Table 2.1 shows some data about it.

Fig. 2.1
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New-Cairo social housing layout, second phase highlighted (Google Earth 2019)

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Table 2.1 Data about Phase 2 of New-Cairo social housing project
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From the field survey and questionnaire to residents some problems are found to be affecting the water efficiency of the project. For example; wide asphalt roads and impervious areas increase the heat island effect in addition to increasing the stormwater runoff. Another example is that green areas are deteriorated due to the lack of irrigation. Furthermore, the main pipelines for water supply are suffering from repeated leakage problems and this causes higher maintenance cost and more excavation works to detect the problems in the pipelines; not only this, but also leakage affects the water supply efficiency in the residential units and the quality of the open spaces as leakage merges them, as shown in Fig. 2.2. There are also leakages in the indoor pipelines which is obvious in the deteriorated finishing materials of the buildings’ façades, as shown in Fig. 2.3. The rainwater infrastructure also isn’t sufficient and after an event of rain; stormwater floods the spaces as shown in Fig. 2.4. Water sub-metering isn't used for all the residential units and the average water consumption for each unit is estimated to be 30 m3/month, approximately 250 L/person/day; all residential units must pay for 30m3/month although there is no water sub-metering. From questionnaires it was found that most units didn’t have meters yet, and this makes residents don't give interest to the amount of water they consume because whether the consumption is high or low; the same amount of money must be paid.

Fig. 2.2
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Leakage merging spaces (Author 2019)

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Fig. 2.3
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Deteriorated facade (Author 2019)

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Fig. 2.4
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Rainwater flooding spaces (Author 2019)

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According to the survey and field measurements it's found that the devices used for each unit are 1 bathroom tap 8.3 L/min, 1 kitchen tap 8.3 L/min, 1 shower 9.4 L/min, 1 single flush toilet 6 L/flush and 1 toilet tap 3 L/min. By using LEED indoor water use reduction calculator and assuming four persons in each residential unit and using the default time of use and number of uses, it was found that the baseline water consumption is about 188 L/day/person. From questionnaire to residents it was found that the water use is more than that amount, and is almost the same as the data approved by the water company. It was found that the average of the actual water number of uses and time of uses for the faucets was higher than the defaults of the LEED indoor water use reduction calculator and by entering those data to the calculator, it was found that the average water consumption/person is 238 L/day and for each residential unit is about 952 L/day; as shown in Table 2.2.

Table 2.2 Actual water consumption/residential unit in New-Cairo social housing
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The green areas in the project are deteriorated but it has an area of about 54,000 m2. By using LEED V4 outdoor water calculator and entering the monthly precipitation rates in Cairo, which ranges from 7 mm in January to 0 mm in August, in addition to areas of 12,000 m2 trees, 15,000 m2 shrubs and 27,000 m2 turf grass and fixed-spray for irrigation, it's found that 348,923 L is the water requirement/month; and the percentage of reduction from baseline is − 157%, according to the LEED V4 calculator; as shown in Table 2.3 and this explains the reason behind its deterioration.

Table 2.3 Outdoor water consumption for the total landscape area for New-Cairo social housing
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3.2 Opportunities for Improving Water Efficiency in New-Cairo Social Housing Project

There are some strategies that could be implemented in this project to improve water efficiency. In the case of using bathroom tap aerators 3.8 L/min and shower aerator 6 L/min and dual flush 3 and 6 L/day; the total water use/unit will be 630 L/day/unit, which is a 34% saving from the actual water use, as calculated by LEED v4 indoor water use reduction calculator as shown in Table 2.4. From the accounting of the LEED indoor water reduction calculator; the actual water consumption for lavatory tap and shower tap is 636 L/day/unit; so this amount of water could be considered graywater and could be replaced with the potable water used for flushing which is120 liters/day/unit; and for irrigation.

Table 2.4 Water consumption when using aerators and dual flush for New-Cairo social housing
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Although the precipitation in Cairo is considered rare but it couldn’t be neglected as it causes serious problems and loads on the infrastructure, the precipitation is 28 mm/year which is 28 L/m2. Assuming using a rainwater harvesting system with efficiency of 75% and as each building roof has an area of 360m2; so the amount of rainwater harvested from the building’s roof is about 7560 L/year/building; theoretically this represents 21.6 L/day/building and 0.9 L/day/unit. The impervious areas in the project represent 42% of the total area which is about 59,488 m2; by assuming using a stormwater harvesting system with an efficiency of 75%; so theoretically 1,249,248 L/year could be available for non-potable water use annually.

When adopting efficient landscaping; LEED V4 outdoor water use reduction calculator showed that in the case of using only drip irrigation the amount of water needed for irrigation will be 252,000 L/month. While in the case of using drip irrigation and replacing turf grass with ground cover and using native plants which had a low water demand, the water demand will be 168,000 L/month and percentage reduction from the baseline is – 24%; as shown in Table 2.5.

Table 2.5 Water consumption for irrigation in the case of adopting efficient landscaping for New-Cairo social housing
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4 Case Study 2—Paraisópolis Social Housing Project in São-Paulo, Brazil

Brazil holds 12% of the world’s freshwater resources and has a water availability of 41,603 m3/capita/year. Freshwater resources distribution is unequal; 70% of the available freshwater resources are located in the Amazon basin, where less than 7% of the population live, while more than half of the Brazilian population lives in the catchments of the Atlantic coast and faces water scarcity problems (Milano and Reynard 2018). In the state of São-Paulo the water balance is critical due to high demographic density, insufficient infrastructure, poor water quality and the effects of climate change. São-Paulo, where more than 20 million people live, was affected by an unpredictable drought during 2014 and resulted in urban water supply shortages in 2015. In 2014, the state of São-Paulo recorded the driest and warmest year since 1961; the precipitation was 830 mm compared with 1681 mm on average over the 1981–2010 and a mean maximum temperature of 31.4 °C in comparison with 28.7 °C on average during the period from 1961 to 2015. Combined with high evaporation rates as reservoirs aren't covered, this resulted in low water levels, fluctuating around 5–15% of their full capacity. In addition to that; polluted water from domestic and industrial effluents are flowing into water bodies. According to some studies the water/capita usage in Sao-Paulo in 2011 was about 180 L/day, and in 2016 was about 120 L/capita/day. São-Paulo loses over 20% of its treated water due to the leakage from pipes before it reaches the taps of the residents (Biswas and Tortajada 2016).

The case study is located in the Paraisópolis neighborhood in the south of São-Paulo city. The climate in São-Paulo is subtropical. The average annual temperature is 19.3 °C; the annual precipitation is 1454.8 mm. Due to climatic changes; wet season has shortened and less rain falls each year. During the wet season, floods occur throughout the city, but in the dry season the entire city suffers from drought. Paraisópolis neighborhood is informal and so most of the infrastructure isn't regulated as it's in the rest of the city. Most houses are connected to the water grid, but not all connections are legal and safe, and not all houses are connected to the sewerage (Velden 2016).

4.1 Water Efficiency Assessment of Paraisópolis Social Housing Project

The Paraisópolis social housing complex was developed as a part of the inventory project carried out by São -Paulo city hall as a part of the urban development plan. The project consists of seven condominiums, the first five A, B, C, D and F were delivered between 2009 and 2011 and condominiums E and G were delivered in 2013 and 2012, shown in Fig. 2.5.

Fig. 2.5
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Paraisópolis social housing layout, condominiums E and G highlighted (Google Earth 2019)

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The design of the condominiums is formed by linear blocks divided into connected modules and having varying heights, depend on the relation of the building with the land slope, all buildings have at least four floors above the ground floor and one to four floors below the stepped ground floor. Condominiums E and G are gold certified by “Selo Casa Azul” and the study will focus on those two condominiums; Table 2.6 gives some data about it. The project followed some criteria for water management; some are mandatory for the certification; like water sub-metering, dual flush toilets and permeable areas; while some are optional like rainwater retention system, water flow regulator and tap aerators (Carvalho 2018).

Table 2.6 Data about condominiums E and G in Paraisópolis social housing project
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The design of condominiums E and G aimed at decreasing the area of the impervious surfaces and not providing spaces for car parking or car access inside the condominiums while limiting the impervious areas to the main road between the condominiums and small areas of concrete pedestrian paths, as shown in Fig. 2.6. This was done to not only achieve water management, but also to encourage using public transport and reduce pollution. There is a rainwater and stormwater retention system as shown in Fig. 2.7; but unfortunately the water harvested isn’t reused as this system is limited to retain the water in order to prevent flooding. Water sub-metering is used for each residential unit; in addition to separated meters for the irrigation. From the field surveys it was found that apparently there are no problems with water efficiency and from questionnaire to residents it was also found that there are no leakage problems or problems related to rainwater or stormwater management.

Fig. 2.6
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Green areas and narrow pedestrian walks (Author 2019)

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Fig. 2.7
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Stormwater collection (Author, 2019)

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From field measurements for condominiums E and G, it's found that the water devices used in each residential unit are 1 lavatory faucet with aerator 3.8 L/min, 1 kitchen faucet with aerator 3.8 L/min, 1 low flow showerhead 6 L/minute and dual flush toilet. By using LEED indoor water use reduction calculator and assuming 4 persons for each residential unit and using the default time of use and the number of uses of the calculator, it was found that the average of the default water consumption/person is about 108.5 L/day. From questionnaire to residents and water bills; it was found that the actual water consumption is lower than the default water consumption; and by using LEED V4 indoor water use reduction calculator, it was found that the average water consumption/person is about 77.2 L/day as given in Table 2.7.

Table 2.7 Actual water consumption/residential unit in condominiums E and G
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The green area is about 3000 m2 for condominium E and G, when considering having 600 m2 trees, 1000 shrubs and 1200 m2 turf grass and fixed-spray for irrigation. By using LEED V4 outdoor water calculator and entering the monthly precipitation rates in São-Paulo which ranges from 293 mm in January to 39 mm in August; it was found that the water requirement for irrigation is about 96,923 L/month and the percentage reduction from baseline is 94%, as given in Table 2.8.

Table 2.8 Outdoor water consumption for the total landscape area for condominiums E and G
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4.2 Opportunities for Improving Water Efficiency in Paraisópolis Social Housing Project

Water efficiency is considered in the project, stormwater is well managed and indoor water use is regulated, despite that there are some strategies which could increase the water efficiency. According to Table 2.7, the graywater available from showers and lavatory taps in each residential unit is about 158 L/day/unit; this amount of water could be used for flushing which are 90L/day/unit or for irrigation. When using a rainwater harvesting system for the roofs with an efficiency of 75% and where the area of the roofs is about 200m2 and the annual precipitation is 1454.8 mm, so the amount of water collected for each building is 283,686 L/year which is 11,626 L/unit/year; and this water could be used for flushing or irrigation. In the case of using drip irrigation, there will be a saving of about 28%, according to the results of LEED V4 outdoor water use reduction calculator; as the landscape water requirement will be 70,000 L/month; as given in Table 2.9.

Table 2.9 Water needed for irrigation when using drip irrigation in condominiums E and G
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5 Results

In New-Cairo case study, it was found that some strategies could be integrated to reduce indoor water use. The most effective strategy in reducing indoor water use was using efficient devices as this will reduce the actual water use by 34%, second was the graywater reuse for flushing by a 12.6% reduction in actual water use and third was rainwater harvesting for flushing by a 0.01% reduction in actual water use. And in the case of combining between using efficient device and graywater reuse for flushing; the savings will be raised up to 47%. For the outdoor water use, it was found that graywater could cover all the irrigation needs. When using plants with low water demand, replacing turf grass with groundcover and using drip irrigation water savings will reach 48%. Rainwater harvesting from roofs could save about 5% and stormwater harvesting could save 30% of the water needed for irrigation.

In Paraisópolis case study, when comparing condominiums, A, B, C, D and F with condominiums E and G; it was found that there is about 40% reduction in indoor water use in addition to efficient management of stormwater in condominiums E and G. From the previous assessment it was found that graywater could cover 100% of the water needed for flushing and could achieve a 30% reduction from the total indoor water use. While rainwater could cover one third of the water needed for flushing and 10% from the total indoor water use. Furthermore; using efficient devices resulted in a 31% reduction from the total water consumption in condominiums E and G compared with the other condominiums. Using rainwater harvesting was found to be more efficient when used for irrigation as it could cover 100% of the water needed for irrigation, while graywater could cover 86% of it.

When comparing the results of the two case studies; it was found that the water consumption is affected by many variables like the water strategies used, social behaviors, country policies and regulations regarding water and climate. The actual water consumption/person in New-Cairo is 67% higher compared with the actual water consumption/person in Paraisópolis social housing. When comparing the efficiency of each water conservation strategy in reducing water use in the two projects it was found that there are some variances.

6 Discussion

Social housing projects deal with very limited resources and it's important to consider water conservation when developing such projects. But when resources conservation isn’t considered and in an attempt to reduce the upfront costs in social housing, the selection of strategies doesn’t always go hand-in-hand with achieving water efficiency or with minimizing environmental impacts. When analyzing the comparison between the two projects an important point must be considered; which is the global domestic production (GDP) to the average of water consumption/capita in each country as it reflects how critical the water situation is in each country. The GDP of Brazil is four times higher in Brazil than in Egypt while the average water consumption/capita is 2.5 times higher in Egypt compared with Brazil.

The results show that water efficiency isn't only affected by the technical aspects; but also by environmental, social and economic aspects, it's influenced by social behaviors, by climate, by technical ways used in the operation, by urban context, site selection and by the overall sustainability of the project. Urban choices and selecting the site of the project in a location with sufficient infrastructure to handle the load of the project is important to ensure a good water management in social housing projects. In the case study of New-Cairo; selecting the site in a location with some problems in the wastewater and stormwater systems resulted in water leakage and stormwater management problems in the project. In Paraisópolis case study, no problems regarding the water infrastructure appeared, this could be due to selecting the location in a pre-developed area with sufficient infrastructure. Furthermore, the urban design and the design of buildings affects the water consumption as providing shade for the façade and outdoor spaces helps in achieving thermal comfort and in reducing heat gain, and consequently reduces the need for using more water in hot days. In addition, reducing the impervious areas and increasing the green areas is effective in handling stormwater.

Although the areas of the residential units are different in the two case studies; but both residential units have an average of four people living in it, in addition to one kitchen and one bathroom. Using water pressure regulators, tap aerators and dual flushing helped in reducing the direct water use; in addition to using water meters which made the residents care more about the amount of water they use; contrary to what happens in New-Cairo social housing. Those measures adopted in the case study of Paraisópolis combined with the country’s regulations made the residents more aware of the water situation. Differences in the climatic conditions between New-Cairo and Paraisópolis might also lead to this variability in the water consumption. For example, in New-Cairo the weather is hotter and more arid, which indeed leads to more water use, combined with some social practices like using excessive amounts of water for cleaning and some design aspects like not considering shading for the open spaces and treatments of facades to reduce heat gain.

For indoors; rainwater harvesting was more effective for indoor water reduction in Paraisópolis than in New-Cairo due to the climatic conditions and the rainfall patterns in each city. While graywater recycling had the same ability in the two case studies to cover all the water needed for flushing with larger impact in Paraisópolis social housing, as the water used for flushing represents 29% of the total indoor water use in Paraisópolis and represents 12.6% in New-Cairo social housing. Water efficient devices had the highest rate of water savings in the two case studies due to the average of water consumption in each project and the residents’ awareness; but the savings were higher in Paraisópolis social housing.

For the outdoor water use in New-Cairo case study, the average water use/m2 is about 6.5 L/month, and for Paraisópolis case study is about 32.3 L/month; although in the first case the reduction from water baseline is -157% and in the second is 94% but this depends on the rainfall patterns and the evaporation rates in each climatic zone. It was also found that for the case study of New-Cairo, graywater could cover all the irrigation needs, while rainwater harvesting in Paraisópolis is more efficient than in New-Cairo and drip irrigation could have an average savings of 30% in the two projects. The efficiency of graywater recycling is higher in New-Cairo social housing, but this doesn't mean that it’s better; but it reflects the high water consumption as the more water you use the more graywater you will have. Furthermore; the amount of stormwater, which could be collected is higher in New-Cairo social housing and could cover all the irrigation, this also doesn’t mean higher efficacy but it reflects the effect of the large impervious areas which lead to more runoff.

For the case study of Paraisópolis in condominiums E and G, the average water consumption/person in indoors is considered optimal. Rainwater and stormwater management is achieved through green areas and a rainwater retention system, but using graywater for flushing and rainwater for irrigation will improve the efficiency and reduces the loads on the water infrastructure. Rainwater for irrigation will not require much fittings as the rainwater retention system already exists; while adopting a graywater recycling system for flushing will make the water consumption/person/day about 55 L.

In order to improve water efficiency in the case study of New-Cairo it's recommended to use graywater for irrigation in addition to integrating between using water efficient devices and reusing graywater for flushing in indoors, this can reduce the average water consumption to 113 L/person/day. In the case study of New-Cairo; harvesting rainwater and stormwater would not be very efficient due to the climatic aspects, so it's recommended to improve the quality of the open spaces and adopt green infrastructure solutions to manage rainwater and stormwater like green roofs and bioswales, which will also improve the environmental aspects and reduce heat gain in the open spaces. In addition to using water efficient technical strategies, there is a need for raising the residents’ awareness about the importance of reducing water use. There is a need also for implementing some environmental solution for the building design to reduce the heat gain through facades and get benefit of the high solar radiance in the location by using solar energy for heating water. Furthermore, using water sub-metering is necessary as an incentive way to make people use less water; even though it doesn’t have direct impact on the water consumption but it affects the people’s behaviors. In addition to this, using leakage sensors will save water, time and energy as it reduces the effort needed to detect leakages (Figs. 2.8 and 2.9).

Fig. 2.8
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Water consumption in liters/person when using conservation strategies (Author 2020)

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Fig. 2.9
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% Water reduction when using conservation strategies (Author 2020)

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7 Conclusion

The whole country’s policies and regulations regarding water are reflected on the water consumption of people. In Egypt and Brazil, where water scarcity is threatening their future; adopting water efficient strategies are of main interest; while in Brazil there are some examples of water conservation in Egypt, the situation is still unsatisfactory. From the assessments of the two case studies, it was found that each project has its own opportunities and challenges depending on environmental, social and economic aspects.

Achieving water efficiency in social housing projects in developing countries; requires co-operation between people, architects and duty bearers. Generally, integration between more than one water efficient strategy and integrating green infrastructure enhances the sustainability of the project on the environmental, social and economic levels. Environmentally, the reduction in water use will lead to a reduction on the pollutants held to freshwater resources; also using green infrastructure will improve the efficiency of the indoor and outdoor spaces. Socially, water conservation strategies will help in raising awareness among people about the importance of rationalizing consumption and its effect on the project particularly and on water resources globally. Economically, adopting water conservation strategies will reduce the demand on freshwater resources and the load on the waste water system and consequently the load on energy; this will also reduce the maintenance costs.