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Water quality indices for rainwater quality assessment in Bandung urban region

Water quality indices (WQI) using STORET method has been used to assess rainwater quality in the Bandung urban regions, based on monitoring data at three locations (Coblong, Sumur Bandung, and Buah Batu). Rainwater samples were analyzed by detecting pH, SO42-, NO3−, Cl−, and heavy metals (As, Cd, Cr, Pb, and Zn) compared with Indonesian Government Regulation No. 82 Year 2001. Rainwater quality showed polluted based on the parameters of the water quality indices analysis using the Class I and Class II criteria. Rainwater quality in Bandung urban region were lightly polluted (Coblong) and moderately polluted (Sumur Bandung and Buah Batu). Rainwater can potentially become a water sources alternative for domestic use and urban farming in Bandung urban region, but it requires further treatment for better quality.


Introduction
The water quality indices is a single number to state the quality of water sources, the determination of water quality indices is carried out through 4 (four) steps: (1) parameter selection, (2) parameter transformation which transforms unit differences and dimensions to the general scale, (3) parameter weighting, and (4) aggregation of sub-indices to produce the final indices value [1].
The research on the water quality indices in Izombe of Niger Delta Region in monitoring the level of rainwater pollution and borehole water as the primary water source in the region compared to the drinking water quality standards from World Health Organization (WHO) showed that the parameters of temperature and color in rainwater exceeded WHO standards for drinking water. The results of analysis showed that the pH of rainwater samples was acidic with a pH range of 5.1˗6.4 (average 5.8). This indicated that the rainwater was more acidic than borehole water [2].
The rainwater analysis in Africa to identify rainwater parameters as compared to water quality standards from WHO showed that rainwater in the Metropolis City of Uyo was not safe for drinking, where the total value of Pollution Index (PI) had indicated presence of Ni, Cd, Pb, and Fe which caused rainwater have a risk when consumed [3].
The use of rainwater in Indonesia has been regulated according to the Regulation of the Minister of Environment No. 12 Year 2009 about Rainwater Utilization were activities to collecting, using, and adsorbing rainwater into soil as groundwater conservation. Rainwater as raw water in Indonesia must meet water quality standard requirements based on Government Analysis of the water quality indices on raw water sources, especially rainwater, has shown that the water quality indices analysis method can produce recommendations regarding the feasibility of using rainwater as raw water for drinking water and domestic needs.
The Bandung urban region has high rainfall every year between 2,000-3,000 mm/year, but rainwater utilization must consider the potential contamination from air pollution due to human activities and industrialization both local and long-distance pollutant sources. Therefore, the water quality indices analysis can be used as a method for rainwater quality analysis in the Bandung urban region. This paper aims to explain the results of rainwater quality indices analysis in the Bandung urban region using the STORET method to determine the feasibility of rainwater before being utilized.

Rainwater analysis
The pH of rainwater varied between 3.0-7.5 pH units, as measured using a pH meter with a measurement accuracy of ± 0.01 pH units at a measurement temperature of 25 o C. The pH meter has been calibrated with standard solution of pH 4, pH 6.86, and pH 10.

Data Analysis
STORET refers overall to "STORage and RETrieval" was an electronic data system for water quality monitoring data developed by EPA. The STORET method is one commonly used method for determining the status of water quality in Indonesia. This method identifies which parameters meet or exceed water quality standards. The STORET method compares the water quality data with the adjusted water quality standard to determine water quality status.
The parameters analyzed to obtain indices values were pH, SO 4 2-, NO 3 -, Cl -, As, Cd, Cr, Pb, and Zn. The parameter values were then compared with water quality criteria according to Government Regulation No. 82 Year 2001, as described in Table 1. The water quality classification used in this study was Class I and Class II criteria. Class I, is the raw water designated for drinking water, and/or other designation which requires water quality that is the same as the utility. Class II, is the water designated for water recreation facilities/ infrastructure, cultivation of freshwater fish, livestock, water for irrigating plantations, and/or other designations that require water quality that is the same as those uses. Thus, it is expected that rainwater can potentially be used as an alternative for raw water for drinking water and other domestic needs such as irrigating plants in urban regions (urban farming).
The determination of the status of water quality is through the value system from USEPA by classifying water quality in four classes, as described in Table 2. The classification of water quality base on STORET index were good condition, lightly polluted, moderately polluted, and heavy polluted.

Rainwater concentration
The concentration of rainwater parameter based on the result of data collection shows in Table 3. The results showed that the pH of rainwater in the Bandung region wass 3.

Rainwater quality indices
Rainwater quality indices in Bandung urban region base on STORET method showed different quality status indices between different location, because of small spatial difference in this region. The rainwater quality indices result shows in Table 4. The rainwater quality indices at Coblong region based on the STORET calculation is categorized as lightly polluted with a score of -10. Parameters that did not meet Class I and Class II criteria were minimum pH value (3.13), average pH value (5.4), and maximum concentration of Pb (0.153 mg/L). Other metal parameters, Cd in Coblong region showed that the maximum concentration did not meet the quality standards Class II (0.011 mg/L). Rainwater quality indices in Sumur Bandung region was categorized as moderately polluted with a score of -20. Parameters that did not meet Class I and Class II criteria were minimum pH values (4.10), and average pH value (5.50). On the other hand, the parameters of heavy metals that did not meet the quality standards Class I and Class II criteria were maximum concentration of Cd (0.014 mg/L), Rainwater quality indices in Buah Batu region was categorized as moderately polluted with a score of -12. Parameters that did not meet the Class I and Class II criteria were minimum pH values (4.3) and average pH value (5.52). The parameters of heavy metals that did not meet the quality standards Class I and Class II criteria include maximum concentration of Pb (0.110 mg/L), maximum and average concentration of Zn (0.665 and 0.022 mg/L). The heavy metal of rainwater especially Pb and Zn in Sumur Bandung region was influence of local emissions of motorized vehicle activities in Bandung urban centers, while Zn emissions in Buah Batu region was possible from local industries emission. Coblong region was an urban area with a densely populated and dominated by domestic activities. The differences of rainwater in 3 (three) region in Bandung urban area were impacted of different landuse.
The dominant anthropogenic sources of heavy metals in rainwater represent coal combustion, automobile exhaust, and industrial emissions [5,6,7,8]. Heavy metals from rainwater accumulate in the biosphere and may cause adverse human health and environmental effects [9,10].
Exposure to extreme water pH values on human health can irritate the eyes, skin, mucous membranes, and gastrointestinal tract in sensitive people. A pH value of less than 4 can cause red eyes and irritation, and if the pH is less than 2.5, it will cause irreversible and extensive damage to the epithelial tissue [11].
EPA explained that the solubility of oxides of nitrogen and sulfur dioxide in acid rain is related to health problems, especially irritation of the eyes and lung diseases such as asthma and bronchitis, NO x is a significant contributor to the formation of ozone in the atmosphere which also has disruptive health effects on resources such as contaminating food and water.
Rainwater utilization, such as rainwater harvesting systems, must pay attention to regional characteristics such as topography, season conditions, and air pollutants that can be sources of rainwater contaminants and their effects on health [12,13]. The rainwater can then be used for drinking water, agricultural irrigation, urban greening, and other needs that require good water quality [14].

Conclusion
Determining rainwater quality in the Bandung urban region was important before rainwater was using for water resources of drinking water or other uses such as agriculture in urban regions (urban farming). Utilization of rainwater, it must pay attention to the quality of rainwater in each urban region despite the results of the analysis of rainwater quality showing the presence of heavy metals and do not meet the quality standards for Class I and Class II criteria. This is due to prevent the impact of rainwater utilization on human health. Therefore, with the detection of heavy metals such as Pb in rainwater, the possibility of Pb accumulation must be considered, especially in plants if consumed directly.