Today, the growing population on the one hand, and the limitation of fresh water resources, on the other hand, have led to an assessment of water quality in terms of quality and quantity, especially in arid areas, in a special place in groundwater studies. So that the supply of water needed for drinking with proper quality and without any kind of pollution, has become a human challenge. One of the indicators for assessing water quality is the concentration of the main ions in water. The concentration limit for these ions in drinking water has been determined by the World Health Organization (WHO). One of the most commonly used methods for assessing drinking water quality is the Schuler diagram, which allows water to be checked at a specific point in the area. Hence, the five selected samples representing the entire aquifer are in good quality. But, in order to investigate the spatial variations in drinking water quality across the entire aquifer area, the Groundwater Quality Index (GQI), presented in 2007 by Babyker et al., Was also used. The results of this study showed a value of 74 to 95 percent, the groundwater of the studied plain has good drinking quality standards.

This study aim was to evaluate the relationship between the drinking water quality in Arak city regions and the drinking water sources to identify areas with inappropriate quality drinking water and its zoning with the geographic information system (GIS) and planning to address drinking water quality problems. In this research, drinking water from 18 areas in the city was sampled to measure physical and chemical parameters during 2016. Parameter analysis was carried out by the standard water and wastewater. To extract the contamination maps, IDW method was used in GIS environment. The drinking water quality parameters average  for pH, TDS, EC, TH, F, Cl, NO3 and SO4 was 7.4, 50.67(mg/l), 28.840(µS/cm), 28.38(mg/lCaCO3), 17.0(mg/l), 15.95(mg/l), 19.66(mg/l) and 27.49 (mg/l) respectively. The results showed that the highest concentration of pH, TDS, and EC was in the east.  TH is located in the south. The highest amount of F is in the west of the city and F is highest in the south, the highest NO3 and SO4 are located in the south. In general, the comparison of measured values ​​with the set value indicates that the average value of all elements was lower than national standards, but the mean of TDS, TH, and NO3 is higher than global standards.

In this research، an innovative drinking water quality index for assessing water resources as “modified drinking water quality index (MDWQI)” was developed and applied for evaluating all of the groundwater resources utilized for community water supply in urban areas of Iran during 2011. Twenty-three water quality parameters and relevant Iranian standards for drinking water quality were selected as input parameters and benchmarks respectively. The MDWQI is calculated using three factors including the number of parameters that excurse benchmarks، the number of measurements in a dataset that excurse benchmarks and the magnitude of excursions. The MDWQI scores range from 0 to 100 and classify water quality in five categories as excellent (95-100)، good (80-94)، fair (65-79)، marginal (45-64)، and poor (0-44). According to the MDWQI value، about 95% of the groundwater resources were in the good condition and the others were in the fair or marginal condition; also the best and the worst water quality of water resources were observed in Ardebil Province and Qom Province respectively. The three parameters of fluoride، magnesium، and nitrate recorded the highest rates of violation to be 74، 32، and 13% respectively. The nationwide average score of the MDWQI was 85 (good description). This study indicated that the MDWQI and its sub-indices could describe the overall water quality of water bodies easily، reliably and correctly and have the potential suitability for extensive application all over the world.

Assessing the quality of water resources is an important aspect of improving their management. Given the importance of groundwater resources in the Qazvin Plain, and to have a better understanding of the status of these resources, this study has focused on examining the quality of groundwater for drinking and agricultural purposes. For this purpose, using hydrogeochemical parameters, two quality indicators for drinking water and irrigation were selected to investigate and study the quality of groundwater in the years 2012, 2016, and 2020. Based on the results, quality indicator maps for drinking and irrigation water were classified, and the percentage of each class's area and their average values were obtained for different land uses using ArcMap 10.8.2 software, to consider the mutual effect of land use on groundwater quality. The results showed that the average drinking water quality index in the years 2012, 2016, and 2020 were 135.02, 128.30, and 127.38 respectively, indicating an improvement in drinking water quality. The average groundwater quality index for irrigation in recent years was 62.21, 63.51, and 63.39 respectively. Generally, the quality of groundwater for drinking and agricultural purposes in the northern regions was better than in the southern regions, while the groundwater in the central and eastern parts of the plain, which includes abandoned and neglected lands, has become increasingly restricted for irrigation over time. The results demonstrated that the area of land with suitable quality groundwater for drinking is decreasing. During the study period, the area of good class has decreased, while the area of poor class has increased.

Water quality determining in water resources evaluation is significantly important and its monitoring and zoning are key factors which should be considered in town planning. The aim of this study is identifying the most appropriate interpolation method for water quality determining by using Schuler and Will Cox diagrams in drink and agriculture sectors. Over this study, 22 piezometric wells are used in an unconfined aquifer located in Malayer plain. To determine the quality of drink and agriculture water, Schuler and Will Cox diagrams that are the most common classification methods are used respectively. Geostatistical methods that namely Kriging, Co-kriging and Inverse Distance Weighing (IDW) are used in GIS for water quality zoning in the study area and their results are compared to each other as well. The results showed that the simple Co-kriging technique (spherical) is the most appropriate interpolator for interpolating and zoning the drink and agriculture water quality. Investigation of drink water quality based on Schuler diagrams with considering TDS and TH parameters showed that the drink water quality is divided into three groups; good, acceptable and inappropriate. In the agriculture sector based on Will Cox diagrams using EC and SAR parameters, agriculture water quality is measured into two groups; good and average.

Fuzzy evaluation presents a certainty level for the acceptability of water for drinking purposes based on prescribed standards of various organizations and perception of the experts. In this study, fuzzy set theory was applied for decision making on the suitability of certain groundwater resources for drinking purposes based on chemical quality. The quality of water was expressed in indefinite environment of monitored data and prescribed standards given in a nonprobabilistic sense. From the 9 cities in Esfahan Province, 29 groundwater samples that were collected from the drinking water wells are used in this study. These samples were analyzed for 11 chemical parameters. But, finally 9 parameters were used for evaluation of drinking water quality. The results showed that 10 water samples were in the “desirable” category with a certainty level of 84-97%, 9 samples were in the “acceptable” category with a certainty level of 50-100%, and 10 samples were in the “nonacceptable” category with a certainty level of 50-95%. Furthermore, about 65% of the samples were in the “desirable” or “acceptable” categories for drinking purposes.

Considering the quality of drinking water in human health, an important role should be given to the quality of aquifers as the main source of water supply required for rehabilitation experiences. The purpose of this study was to investigate the groundwater quality required for drinking in the northeast of Bijar plain with GQI index using GIS software. Study area of Bijar plain aquifer is one of the aquifers of Kurdistan province, which is the source of drinking water in part of Bijar city and affects more than 12 villages.. Drinking water quality index was prepared using four methods GQI, GQI-GA, GQI-FL-GA and GQI-FG for this aquifer and then the correlation coefficient and RMSE were used to validate and compare the results of the four methods. Based on the obtained results, GQI-FL-GA method with correlation coefficient of 0.89 and RMSE 0.01 showed the best results and GQI-FG method with correlation coefficient of 0.86 and RMSE 0.11 presented the weakest results. According to this method, about 8.8 and 91.2 percent of the plain has acceptable and suitable quality, respectively, that most of the northeastern parts that are the output of the plain have lower quality than other areas.

Clean drinking water has been identified as the most important factor affecting human health. The main source to control healthy drinking water is the "water quality standard" reports. Due to the fact that each country has its own economic resources, technology, and water characteristics, preparing separate water quality standards are of necessity. This article contains guidelines for the preparation of drinking water quality standards in developing countries. The most important strategies on the field are: laying rules in order to formulate a standard, development of strategies to recognize desired parameter, sampling and monitoring programs, as well as how to apply the standards which are included in the study. Finally, a comparative analysis of water quality standards in a developing country is compared to the standards provided by the World Health Organization and the Environmental Protection Agency.

Nowadays, water quality is one of the key issues in most regions all over the world. Because of its high relation with human health and also have important role in management and exploitation of resources. This research has done first time in Pasargad city located in 105 km of eastern north of Shiraz. In order to determine drinking water quality factors using data mining technique, results of this research have obtained using Quest decision tree in Clementine software(12 version) and showed most effective factors of drinking water in this region is function of total harness and electrical conductivity. In this way, if total hardness in this city is less than 282.232 parts in million and electrical conduction is less than 822.787 micro mohs in centimeter, this water will be suitable for drinking. Therefore recommended more noting to refine and decrease the hardness of water for human drinking water, moreover continuous refining in periodically regular sampling of water resources in this city should be noted.

The main portion of water demands of arid regions like Kashan Plain, Iran supply by groundwater wells. This research was conducted to assess the groundwater quality as well as modelling and mapping groundwater quality in the study area using geosatistics and deterministic techniques. Five water quality parameters, including Electrical Conductivity, Sodium Adsorption Ratio, Total Hardness, Total Dissolved Solids and pH, were applied to determine the irrigation and drinking water quality index using the Wilcox diagram and WHO standards. The final map indicated that the groundwater quality increased from north to south of the study area. The areas located in the centre, south and eastern south of the study area had the optimum quality for irrigation and drinking purposes. Furthermore, based on the results of zoning using the Wilcox diagram determined that ground water quality of the study area 22%, 42% and 36% were good, medium and non-suitable, respectively