Introduction

Water scarcity is an ongoing challenge in both developed and developing nations. The growing global issue of water scarcity impacts nearly 4 billion people worldwide, and by 2025, the United Nations estimated that half of the world’s population will reside in places with a shortage of water (Lifeng Li 2023). Since only 2.5% of the water on earth is freshwater, and a substantial amount of it is trapped in glaciers or underground aquifers, this crisis is even worse than it may seem at first sight. Urbanization, climate change, population increases, and ineffective water management techniques are the main contributors to water scarcity (Krishnakumar et al. 2022).

Population expansion is a leading cause of water scarcity. The need for water supplies has grown with the development of the global population. This is especially true in cities with a high population (Salehi 2022). As they expand, these cities are placing an increasing amount of strain on the region’s water resources. Another significant factor causing a shortage of water is climate change. Water availability in some areas is becoming more erratic as temperatures rise and precipitation patterns shift. This is especially true in dry and semi-arid regions where water is naturally scarce ((Morante-Carballo et al. 2022). Moreover, water scarcity is primarily caused by the inefficient use of water resources; for example, the irrigation systems still used in many countries are old and ineffective, which can result in considerable water losses (Tirtalistyani et al. 2022). Despite the existence of more efficient alternatives, numerous companies continue to utilize significant quantities of water for cooling and various other purposes.

Recently, there has been a rise in the interest in water recycling technology owing to the world’s increasing water shortage and the need for sustainable water management. Water recycling is the process of treating wastewater and reusing it for various purposes such as irrigation, business operations, and potable water production (Gupta et al. 2012). Water that has undergone treatment and processing for reuse is referred to as recycled or reclaimed. Water recycling aims to reduce both the requirements for treated and discarded wastewater and the need for fresh water. This included water from sewage and manufacturing operations. Another type of recycled water is air conditioning (AC) water, which is the water gathered and reused from air conditioning systems. As a result of several factors, such as population expansion, urbanization, climate change, recycled water, and, in particular, AC water, is now becoming a more widely promising water source. The use of these technologies for AC water is particularly pertinent because AC systems use a large quantity of water. AC water-recycling technologies include membrane filtration, biological treatment, and chemical treatment (Gupta et al. 2012). A recent study published in 2024 highlighted several benefits associated with reusing air conditioner condensate. Firstly, it significantly reduces the strain on freshwater resources, particularly in water-stressed regions. Secondly, reusing condensate lowers water bills for households and reduces the energy required for water treatment, as condensate is already relatively clean. Additionally, the reuse of air conditioner condensate reduces the discharge of wastewater into the environment, alleviating the burden on wastewater treatment plants (Matarneh et al. 2024).

Air conditioning systems are frequently employed in buildings and automobiles to create comfortable indoor environments by regulating temperature and humidity. However, contaminants, including bacteria, dust, and chemicals, may be present in water and can harm both human health and indoor air quality. Determining and managing any potential dangers requires an understanding of the biochemical makeup of the condensate water. Bacteria and fungi can flourish in condensate water, thereby contributing to household air pollution (Haleem Khan and Mohan Karuppayil 2012). In addition to causing allergies and respiratory diseases, these microbes can harm and destroy air conditioning systems. Condensate water may also contain metals, such as calcium and magnesium, which can cause scale to form and clog the system (Shah et al. 2019). As a result, air conditioners may operate less effectively and use more energy. Condensate water may contain contaminants such as heavy metals and volatile organic compounds (VOCs). (Shah et al. 2019). The chemicals known as VOCs have been linked to cancer, headaches, and other health issues (David and Niculescu 2021). Moreover, the heavy metals found in contaminated water have been linked to several other health issues, including cancer and damage to the nervous system (Mousavi et al. 2013). These contaminants may originate from industrial emissions, insecticides, and cleaning chemicals (Shah et al. 2019). Various analytical techniques can be employed to analyze the content of condensate water, including the use of molecular methods like polymerase chain reaction (PCR) or culture-based approaches for identifying microorganisms. Additionally, techniques like gas chromatography-mass spectrometry (GC-MS) and inductively coupled plasma mass spectrometry (ICP-MS) can identify chemical elements and contaminants (Kumar et al. 2022). The composition of condensate water from air-conditioning systems can have a substantial impact on the efficiency of the systems and the well-being of occupants in the building. Saudi Arabia, located in Southwest Asia, is the largest nation on the Arabian Peninsula. In terms of geography, Saudi Arabia primarily comprises desert regions. As a result, SA faces a water crisis. SA depends mainly on two main sources for water acquisition, the first being water desalination plants whilst the second source being ground water (Alrwis et al. 2021). Fortunately, Saudi Arabia benefits from a large amount of groundwater and seawater, and to make this water suitable for human consumption and industrial use, it depends primarily on desalination. However, water desalination incurs high manufacturing and operating costs. Therefore, to address the growing water demand in Saudi Arabia’s municipal, industrial, and agricultural sectors, it is crucial to explore alternative water sources. In recent decades, natural resources have been extensively studied to investigate the potential of treating wastewater as a non-conventional solution to alleviate water scarcity. However, it remains an unsafe source because of the difficulty in removing all medicines and antibiotics (Wu et al. 2015). Alternative solutions, especially for hot and humid areas, include the extraction of water from the air (Cattani et al. 2018). Saudi Arabia, being a hot and dry country, relies heavily on heating, ventilation, and air-conditioning (HVAC) systems. These HVAC systems produce a significant volume of condensate. Consequently, in the pursuit of a cost-effective alternative source, air conditioners (ACs) have emerged as a viable option for generating clean water. Typically, AC condensate, which is usually discarded via sanitary drains, has been recognized as a potential valuable resource. Moreover, for condensate water conditioning systems to be viable, the volume and quality of the produced water must meet specific criteria, ensuring its suitability for both domestic and agricultural applications. Despite its potential benefits, the reuse of air conditioner condensate also presents certain challenges. One significant limitation is the potential presence of contaminants, including airborne pollutants and microbial organisms. Thus, until now, it is still not clear if AC condensate water is beneficial for domestic use. The aim of this study is to assess the feasibility of reclaiming condensate water from air conditioning (AC) systems by evaluating the volume and quality of AC condensate water produced by both split and window AC systems. The most common AC systems used in SA are window air conditioners (WAC) and split air conditioners (SAC). Therefore, this study aimed to collect condensate water from these two systems and examine the chemical and biological characteristics of AC condensate water.

Materials and methods

Materials

All chemicals and materials were purchased as summarized herein. Vessels, hose, pipes, and gallons (Local market in Jeddah), ethanol (Saudi Pharmaceutical Industries), glass bottles for collecting samples (Duran Group, USA), drinking water Berain and Pure life (local market in Jeddah), agarose (Norgen Biotek Corp, Canada), 1 kb DNA ladder (New England Biolabs, USA), 100 bp DNA ladder (New England Biolabs, USA), COD, PO4 − 3, Cl−, and SO4 − 2 (Hach Permachem regent, USA), Oligo (27 F & 1492R) (Macrogen, Korea), heavy metals (As, Cd, Cr, Cu, Mn, Ni, Pb, Fe and Zn) (Agilent Technologies, USA), Heavy metal (Hg) (PerkinElmer Pure, USA), nutrient agar and nutrient broth (TM MEDIA, India), crystal violet, iodine solution, ethyl alcohol and safranin (Crescent Diagnostics, Saudi Arabia). All reagents used in this study were of analytical grade.

Method

AC condensate water collection

The study took place from January 2019 to December 2019 in the southern region of Jeddah, forming the study’s geographical scope with geographic coordinates latitude 21.4858° N and longitude 39.1925° E. All materials (vessels, hose, containers, and pipes) for water collection were sterilized before each use. A hose was connected to the outer part of the AC, where the condensate water leaked and collected into a sterilized 35-liter gallon to measure the generated quantity. Condensate water was collected for 8 h daily (9 am–5 pm); this period represents the peak of operation time and a period of high temperature during the day. The amount of water generated within 8 h was recorded. The samples were placed in sanitized one-liter glass containers and kept in a refrigerator at a temperature of 4 °C until they were ready for subsequent analysis. One sample was chosen as a representative monthly sample. Climate factors, including temperature and humidity, were recorded daily. To determine the average quantity of water produced per hour per day, the total quantity was divided by the number of hours. This average value was then multiplied by 24 to calculate the daily volume of water condensate. The physical, microbial, and chemical parameters of the samples were tested. The pH, turbidity, TDS, EC, COD, and chemical substances were included in the physicochemical analyses. The resulting values were compared to those of commercial drinking-bottled water and tap water.

Assessment of condensate water quality

Physical, microbial, and chemical parameters were determined using the most relevant laboratory instruments. Microbial investigations have been carried out to assess the potential presence of bacterial contamination. The resulting values were compared with those of the two brands of drinking water and tap water. The chemical substances were determined ‎using a laboratory spectrophotometer for water analysis (HACH DR 3900). ‎The metering modes for COD, PO4 − 3, Cl−, and SO4 − 2were selected, and the results were recorded for each sample.

Analysis of heavy metals

Inductively coupled plasma optical emission spectroscopy (ICP-OES) was utilized to quantitatively analyze and measure the levels of heavy metals. The standard stock solution used was calibration mix 2 for AA and ICP-OES (125 mL), which contained 100 mg/L Ag, Al, As, Ba, Be, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, Tl, Th, U, V, and Zn in 5% HNO3. The pH was controlled using a Mettler ‎Toledo 320-S pH meter (Mettler Toledo Instruments Co. Ltd., Shanghai, China) ‎ was supplied using a combined electrode. The auxiliary gas (Ar), carrier gas (Ar), and plasma gas (Ar) ‎flow rates were 1.0, 1.0, and 12 L\ min, respectively.

Microbial detection (conventional method)

A full loop of each condensate water sample was spread onto a nutrient agar plate. The colony morphology was described for each plate. Briefly, the culture media were inoculated with (100 µl) of the diluted solutions of each sample and spread on the surface of the medium. All plates were incubated at 37 °C, and growth was monitored for 24 h. Various colonies were selected and transferred to fresh media to acquire pure cultures. The cultures were purified on the same media from which they were isolated, and all isolates were preserved at 4 °C. Simultaneously, the isolates were grown in broth, and 1 ml of culture was transferred to 1 ml of 50% sterile glycerol for long-term preservation at -20ºC. Phenotypic and phylogenetic techniques were used to identify the bacteria at the genus level. Bacteria were identified using morphological, biochemical, and physiological tests as well as molecular biological technology, according to Bergey’s Manual of Determinative Bacteriology. Genomic DNA from each strain was extracted following the manufacturer’s guidelines employing a Key Prep-Bacterial DNA Extraction Kit (QIAamp DNA Blood Mini Kit 50). The extracted genomic DNA was then subjected to gel electrophoresis on a 1% agarose gel to verify its purity. Once the successful extraction of genomic DNA from bacterial strains was confirmed, the conventional method was employed to identify the strains. The 16 S rRNA gene was amplified via PCR using the extracted DNA. Table 1 displays the number of components utilized for the amplification of the 16 S genes.

Table 1 Components of the PCR reaction
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Bacterial universal primers (Forward and Reverse) were used for DNA amplification (Table 2). Primers were purchased from Humanizing Genomics Macrogen (Oligo).

Phylogenetic analysis

DNA sequencing was conducted in Korea by Macrogen, and the phylogenetic classification of 16 S rRNA gene sequences was verified using the Basic Local Alignment Search Tool (BLAST), accessible on the website of the National Center for Biotechnology Information [NCBI; (Altschul 1997)]. The obtained sequences were subjected to error correction using Finch TV software, version 1.4. In Finch TV software, an unknown nucleotide is denoted as N and can correspond to one of the four nucleotide bases (A, T, G, or C), represented by different colors.

Statistical analysis

Data analysis was conducted using Statistical Package for Social Science (SPSS) version 23.0 for Windows (SPSS Inc., Chicago, IL, USA). GraphPad Prism 7 software was used to represent graphs. Correlations between humidity and the monthly amount of water produced by either the WAC or SAC were investigated using Pearson’s correlation coefficient (r). Statistical significance was set at p < 0.05.

Results

Table 3 represents the monthly amounts of water collected from both WAC and SAC. The water condensate was collected for eight hours per day. The total amount of water collected per day and an annual calculation are shown in Appendix A. The results (Fig. 1) show that the amount of water produced by the split AC was higher than that of the window AC. The amount of water generated during October was very high, reaching approximately 2,274 L and 1,146 L per month for SAC and WAC, respectively. This was accompanied by lower temperature and higher humidity. The lowest quantity obtained was in January at a rate of 298 L by the WAC and in February at a rate of 1,292 L per month for SAC. The highest humidity level was approximately 55% in November, and the highest average temperature was observed in June at 40 °C.

Fig. 1
figure 1

Amount of AC condensate water

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A highly significant positive correlation (r = 0.77 and r = 0.73, respectively; P ≤ 0.01) was observed between humidity and the amount of water generated by SAC and WAC (Fig. 2).

Fig. 2
figure 2

Correlation between humidity and water quantity

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pH and turbidity

The pH values of both the WAC and SAC are presented in the Supplementary Data. The pH of tap water (8.10) was higher than that of drinking water (7–8) (Tables 1 and 2 in the Supplementary Data). The results showed that the greatest value of turbidity was found in water collected from WAC at 3.92 (NTU) in October and SAC at 3.22 (NTU) in September. The turbidity value of the tap water was low at 0.63 (NTU). The TDS and EC values for the WAC sample were higher than those of SAC, drinking water, and tap water at 203 (mg/L) and 405 (µS/cm) in December. To measure the chemical parameters, one sample was analyzed for each AC in October 2020, and the results were compared with the standards of the World Health Organization (WHO, 2008) for drinking water quality. The values of PO4-3 and Cl- were almost non-existent in all water sources. No SO4-2 was detected in any of the samples. The highest COD value was found in the WAC water 69.6 (mg/L). (COD values are presented in the supplementary data (Table 3).

Table 2 Oligonucleotide primers
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Table 3 Monthly condensate water in litter (L) from January to December
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Heavy metals assessment

The results show that there was a slight increase in the Pb concentrations in AC water, bottled water, and tap water when compared to the guidelines for drinking water issued by the WHO (WHO 2017). The remaining metals were almost non-existent in all the samples. Table 4 presents the heavy metal content in the AC condensate water collected from January to March. The rest of results are provided in (The supplementary data, Tables 4, 5, 6 and 7).

Table 4 Heavy metals in the 24 water samples from January to March compared with WHO standards for drinking water quality
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Bacterial contamination assessment

Only the samples in which bacteria were detected are listed in Table 5.

Table 5 Sources of samples
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Fig. 3
figure 3

Light microscopy images of the isolates

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The morphological characteristics of isolates A1-1, A2-2, B1-3, B2-4, B3-5, B4-6, C1-7, C2-8, C3-9, and D2-11 were described after growth on nutrient agar medium within 24 h and are represented in the supplementary data. The colonies of all isolates were gram-positive, creamy colored, round, and rod-shaped, except for U stock-10, which was gram-negative. (Fig. 3)

A total of nine bacterial strains were obtained from water samples collected from WAC (Window Air Conditioner) and SAC (Split Air Conditioner), while two bacterial strains were isolated from separate samples of bottled drinking water and tap water. Figure 4 illustrates the molecular weight of the genomic DNA of these strains, assessed through gel electrophoresis on a 1% agarose gel. The size of the DNA molecules was determined using Hyper-ladder 1Kb as a reference marker in these investigations.

Fig. 4
figure 4

Total genomic DNA extraction isolates on agarose gel

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DNA sequencing was performed in Korea by Macrogene, and the phylogenetic ‎determination of 16 S rRNA gene sequences was confirmed for all the isolates—A1-1, A2-2, B1-3, B2-4, B3-5, B4-5, C1-7, C2-8, C3-9, U stock-10, and D2-11—are of one type of bacteria, Bacillus, except for the bacteria cultured from tap water, which was Limnobacter thiooxidans. Bacillus pumilus was found in window AC samples in February and March. It was found that drinking water number 2 and the window AC sample for November contained the same type of Bacillales bacterium (Table 6).

Table 6 Types of bacteria
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Discussion

The Middle East is currently in a water emergency, with Saudi Arabia and different nations of the Gulf Cooperation Council (GCC) grouped by the United Nations as water-scant countries (Tarawneh and Chowdhury 2018). Consequently, inexhaustible surface water and groundwater are inadequate to satisfy the expanding need for water assets for homegrown, industrial, and horticultural purposes (Alrwis et al. 2021).

To the best of our knowledge, this study represents the first attempt to explore the potential for reclaiming condensate water from air conditioning systems. The investigation focused on evaluating the volume and quality of air conditioning water produced by both split and window AC systems, with data collected over the course of one year.

According to the amount of water extracted from condensers of the air conditioners in this study, this can be considered a good source of water that can be used on a daily basis, considering that Jeddah City has a population of approximately 3.5 million and it is expected that the average size of a family is five members. Assuming that there are 5–10 ACs per household, 3–4 million ACs exist in the city. With these assumptions, it is possible to estimate between 6 and 42 m3 of water production per day in January, which is the least amount of water produced in the year for window and split conditioners, respectively. Therefore, large quantities of water can be extracted from Jeddah’s ACs. Thus, the need for agricultural and industrial applications can be met.

The findings demonstrate that SAC systems generated a greater volume of water compared to window conditioners. This disparity in water production between the two types of air conditioners may be attributed to the higher efficiency of split-type units. These results align with the conclusions reached by Algarni and his team (Algarni et al. 2018). The amount of water obtained through window AC was the highest throughout the year. In October, the amount of water collected was the highest throughout the year for both split and window ACs, producing 2,274 L and 1,146 L, respectively. However, our results disagree with the findings of Al-Farayedhi, Ibrahim and Gandhidasan, (2014). The highest production of split AC condensers was noted in August, (99.1 L). This difference may be due to the geographical location or weather. The lowest quantity obtained was in January at a rate of 298 L by the WAC and in February at a rate of 1,292 L per month for SAC. It is assumed that the amount of water extracted from both air conditioners is low in January, but this difference may be due to the leakage or evaporation of SAC water in February.

There is a correlation between the quantity of water generated by both SAC, WAC, and humidity levels. Previous research suggests a significant positive correlation between humidity and the amount of water produced by air conditioners. The water output from both types of air conditioning systems is influenced by humidity, meaning that higher humidity percentages result in increased water production through ACs. (Algarni et al. 2018; Cattani et al. 2018). The findings indicate a significant volume of water being generated by air conditioning systems in Saudi Arabia, presenting opportunities for diverse applications. Moreover, in regions with high humidity, there is potential for implementing a new collection system to harness this water resource effectively.

The World Health Organization (WHO) established a water quality definition in 2008 that includes the various aspects of its physical, chemical, biological, and aesthetic attributes, including factors like its appearance and odor. In the present study, the COD values of the tested samples were in accordance with the recommended values by WHO for drinking water (less than 50 mg\L) except for WAC (69 mg\L). However, for agricultural purposes, all tested samples are within the acceptable range (100 mg\L). Therefore, the condensate water collected from AC can be used for drinking purposes but it is more recommended for agricultural and other domestic uses.

The presence of toxic heavy metals in AC condensate water was found to be negligible overall. However, a slightly elevated level of lead (Pb) concentration could potentially be attributed to contamination from indoor dust. In a previous study conducted by Hassan in 2012, heavy metals in dust collected from Egyptian households, stairs, and entryways were analyzed. The findings revealed that the highest average concentrations of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), and lead (Pb) were observed in the entryway dust, followed by household and stair dust. Hassan (2012) concluded that heavy metals present in household dust could originate from both internal and external sources, as there was a correlation between metal concentrations in household and entryway dust. (Hassan 2012) A previous study conducted in Al-Qunfudah region, Red Sea coast, Kingdom of Saudi Arabia on groundwater found that the mineral values were as follows: Zn (57.90 µg/L), Ni (25.62 µg/L), Cu (7.69 µg/L), Pb (7.11 µg/L), As (4.00 µg/L), Hg (2.04 µg/L), and Cr (1.27 µg/L). All values were higher than WHO standards. This is due to seawater intrusion and heavy metal pollution of the quality of groundwater in the (Alshehri et al. 2021). These values suggest the possibility of using AC condensate water for domestic purposes.

The health of people using the air conditioning is affected by bacterial pollution. Different factors may contribute to bacterial contamination, such as the location of the home, activities of the occupants, frequency of air conditioner usage, and air conditioner maintenance. In the present study, Bacillus pumilus was found in WAC samples and drinking water sample 2. These results were compared with those described in a previous study conducted on a group of 30 randomly selected commercial brands of bottled water from Saudi Arabia, where 18 samples were found to be positive for the growth of the pathogenic bacterium Bacillus spp. (Eid et al. 2017). The rationale for bacterial contamination in only three out of 24 samples of AC water is that it may have been obtained during the preservation of the sample because these bacteria are known to be present in the air and often occur. Another study revealed a notable inverse correlation between bacterial concentration and the wetness level in the filter section. This finding suggests that humidity has a more substantial impact on bacterial growth than temperature. To mitigate microbial contamination, it is crucial to regularly clean and maintain the filters (Li et al. 2017). This clarifies the occurrence of bacteria during months characterized by low humidity and high temperatures. However, research investigating the utilization of Bacillus species for water quality preservation demonstrated that Bacillus effectively reduces the occurrence of diseases and, consequently, upholds water quality. Bacillus contributes to the regulation of various water quality parameters, encompassing physical aspects such as transparency and total dissolved solids (TDS), as well as chemical properties like pH, conductivity, chemical oxygen demand, dissolved oxygen, phosphates, nitrogenous species, hardness, and heavy metals. Furthermore, Bacillus aids in maintaining a balanced microbial ecosystem, thereby reducing the presence of disease-causing microorganisms (Hlordzi et al. 2020).

Collectively, our study validates the capacity of air conditioning systems to generate water through condensation, which can partially fulfill daily water requirements. Additionally, the condensate water from AC units can serve as an alternative water source.

Conclusion

The results of this study hold significant importance and timeliness, particularly in light of the escalating concerns surrounding water scarcity and the imperative to conserve resources. By establishing the cleanliness and safety of HVAC water condensate for consumption, this research contributes to our knowledge on optimizing resource utilization. Furthermore, proposing the incorporation of an additional HVAC tank in new constructions to collect water condensate presents a practical and cost-effective solution with substantial environmental and economic advantages. If implemented, this recommendation has the potential to reduce water consumption, decrease building maintenance costs, and promote sustainable building practices. Through this study, we aspire to support the National Water Strategy 2030, which aims to address challenges and ensure the sustainable development of water resources in the kingdom, while simultaneously delivering high-quality services at an affordable price.