Introduction

Improving water quality in terms of physical, chemical, and biological is one of the priorities of basic human needs. Drinking water consumption is one way to supply the human body’s necessary minerals. Some chemicals, such as pesticides and heavy metals, because of the danger of even small amounts, endanger human health. Therefore, increased awareness in society of the consequences of contaminants in drinking water has created a demand for household water treatment systems which provide higher quality water, and therefore has caused the supply of various kinds and large number of household water treatment systems (Mwabi et al. 2011; Tobin et al. 1981).

Undesirable chemical water quality can cause disorders, such as tooth decay, heart disease, digestive disorders, kidney disease, and high blood pressure. Hence, improving treatment of water resources can play a decisive role in reducing these diseases and their complications. Water-soluble salts are in cationic or anionic forms. Important cations in water are calcium, magnesium, sodium, iron, manganese, and potassium, and important anions are nitrite, nitrate, bicarbonate, sulfate, and chloride (Altura and Altura 1995; Amiri 2007; Ghee and Steel 1991; ISIRI 2009; Maier 2003; Saris et al. 2000; Sauvant and Pepin 2002; Hammer-Sr and Hammer-Jr 2007).

Water treatment systems at point of use (POU) by consumers regularly include the whole range of purification systems, including adsorption, membrane filtration, chlorination, UV lamps, etc., to remove pollutants from drinking water (Chaidez and Gerba 2004). Studies done on the efficacy of POU systems to remove pollutants in laboratory scale have shown that the removal rates of pollutants by these systems are desirable (Coulliette et al. 2013). Based on the World Health Organization’s opinion, water treatment at the point of use is cost effective compared to other methods (Luby et al. 2008).

Because of ion exchange properties, zeolites have extensive uses. Due to the structure and chemical composition of natural zeolites, they can be applied in several research and applications fields, such as ion exchange, adsorption, and desorption of gases, and are also used as a catalyst (Belviso et al. 2014). The zeolite filter is used to remove hardness of water used in household consumption.

Depending on the type of resin, they can remove calcium and magnesium from water, and can add sodium or hydrogen to water. Accordingly, this phenomenon can cause increased salinity or acidity in water and in both cases, may cause or aggravate digestive problems (Yusof et al. 2010; Zhou and Boyd 2014).

Aluminum is a key factor for enhancing chemical absorption and performance improvements. Since aluminum has capacity 3+ and silicon has capacity 4+, replacement of aluminum with silicon causes a reduction in the need for balancing cations (Corma and Garcia 2004). Charged cations balance alkali and alkaline earth metals, such as sodium, potassium, magnesium or calcium. Hydrogen cationic resins can remove all water cations, and anionic resins may also remove all water anions, such as silica (Mao et al. 1994; Wang and Peng 2010).

Miranzadeh and Rabbani (2010) in Iran (Kashan) evaluated the chemical qualities of input and output water of desalination devices. Esmailiyan and Nezamzadeh (2010) in Iran (Ahvaz) in their study showed that surfactant adsorption by zeolite and the production of surfactant-modified zeolite caused extensive changes in the properties of zeolite, and therefore caused changes in absorption of water anionic pollutants. Malakootian et al. (2015, 2016a, b) in Iran conducted researches on the removal of organic and inorganic pollutants, such as acetaminophen and tetracycline, by raw and modified zeolite. Zhou and Boyd (2014) in America in a study showed that mordenite and other zeolites are useful for the removal of ammonia nitrogen from pools. Hortiguela et al. (2013) in Spain in their study showed that natural zeolites are able to reduce fluoride concentration below the limit recommended by World Health Organization. Mwabi et al. (2011) in South Africa studied household water treatment systems used for the production of clean water in South Africa’s low-income communities. Morrisa et al. (2008) in Britain evaluated the effect of water hardness on cardiovascular diseases. Yari et al. (2007) in Iran (Qom) examined the physical, chemical, and microbial qualities of treated-water desalination devices. Monarca et al. (2006) in Italy evaluated the effect of hardness, and calcium and magnesium levels on cardiovascular diseases.

According to research conducted, water treatment systems have the ability to remove minerals, such as magnesium, copper, chromium, fluoride, zinc, iron, selenium, manganese, phosphorus, potassium, and calcium (Yari et al. 2007; Miranzadeh and Rabbani 2010). Because of the popular belief that there is a relation between water purity and some gastrointestinal symptoms, such as bloating and constipation, this study was designed to evaluate the performance of household water treatment systems used in Kerman to remove cations and anions from drinking water.

Materials and methods

The study is a descriptive cross-sectional that was done in Kerman from January to June 2016 on household water treatment systems as a joint project of the Gastroenterology and Hepatology Research Center and the Environmental Health Engineering Research Center, Kerman University of Medical Sciences.

Several devices were selected randomly from all brands of household water treatment systems supplied in Kerman. In cases which the devices were used extensively, samples were selected with filters that had been changed in proper time, based on the device’s operational instructions. The samples were selected from homes in the center of Kerman and also from outwards in the four geographical directions from the center of the city. The reason for this is that in Kerman water is pumped from four sources in different directions with different water quality to the distribution network. Then one sample was conducted of input and output of each device from a total of 30 different brands in homes from the center and four directions of Kerman. In three stages with an interval of 50 days, a total of 180 samples were tested. For each of the samples, some parameters, such as chloride, sulfate, bicarbonate, nitrate, and nitrite, by ion chromatographic method, sodium cations by flame photometer method, calcium and magnesium cations by flame atomic absorption spectrometry method, and total hardness by classic method, were measured. Temperature and pH were measured in situ. The averages of obtained figures from three experiments were calculated. Then the removal efficiency of each of the parameters was calculated, and the results were compared with latest Iran standards and World Health Organization guidelines. Finally, the removal efficiencies of cations and anions were determined for each device and they were then compared with each other. All stages of sampling and testing were done according to standard methods for the examination of water and wastewater, edition 21 (Eaton et al. 2005).

For weighing materials, pH determining, anions measuring, sodium measuring, and calcium and magnesium measuring, an electric scale (AEL-200, Japan Shimadzu), pH meter (HANNA HI2212, Romania), ion chromatography (Metrohm 732 IC Detector, Switzerland), flame photometer (England PFP7, Jenway), and flame atomic absorption spectrometry (YL youngtin8020, South Korea), were used, respectively.

All consumable materials, such as sodium carbonate, sodium bicarbonate, sulfuric acid, sodium chloride anhydrous, the standard solution of calcium and magnesium (1000 ppm), standard solution EDTA (0.01 mM), ammoniacal buffer, and Eriochrome black T indicator were obtained from Merck Company. Data were analyzed using descriptive statistics and SPSS version 22.

Results

In Table 1, the specifications of household water treatment systems supplied in Kerman, the period of use of them, and efficacy of these devices for the removal of anions, such as NO3 −, NO2 −, SO4 2−, HCO3 −, and Cl− from drinking water in Kerman in 2016 are shown.

Table 1 Specifications of household water treatment systems supplied in Kerman and efficacy of these devices in the removal of anions NO3 −, NO2 −, SO4 2−, HCO3 −, and Cl− of drinking water in Kerman in 2011
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The average efficiencies of household water treatment systems studied for the removal of anions, such as NO3 −, NO2 −, SO4 2−, HCO3 −, and Cl− from drinking water were 66.83, 31.50, 85, 67, and 68.43%, respectively. Overall, efficiency in the removal of anions (regardless of the nitrite) in all of the household water treatment systems was obtained at more than 66.83%.

In Table 2, the specifications of household water treatment systems supplied in Kerman, the period of use of them, and efficacy of these devices for the removal of cations, such as Na+, Ca2+, Mg2+, and total hardness of drinking water in Kerman in 2016 are shown.

Table 2 Specifications of household water treatment systems supplied in Kerman and efficacy of these devices in the removal of cations Na+, Ca2+, Mg2+, and total hardness of drinking water in Kerman in 2016
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The average efficiencies of household water treatment systems studied for the removal of cations, such as Na+, Ca2+, and Mg2+, and total hardness of drinking water were 80.23, 61.20, 78.97, and 69.36%, respectively. Overall, performance of the removal of cations and anions in all of the household water treatment systems was obtained at more than 61.20%.

In Table 3, the average removal efficiencies and concentrations of input and output ions of chloride, sulfate, bicarbonate, calcium, magnesium, sodium, nitrites, nitrates, and total hardness of household water treatment systems supplied in each region of Kerman are shown, and also the results of the t test analysis.

Table 3 Concentrations of samples in each region of Kerman and the influence of household water treatment systems in reducing the concentrations of cations and anions in drinking water (mg/L)
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The concentration of ions of chlorine sulfate, nitrate, bicarbonate, calcium, magnesium, sodium, and total hardness had decreased in the output water of water treatment systems. An increase in nitrite production was observed in the output of some devices.

In Table 4, average chemical qualities of water sources in Kerman are reported in terms of various parameters and in comparison with the national Iran standard (ISIRI 2009), Environmental Protection Agency (EPA 2004) and WHO guidelines (WHO 2006).

Table 4 Specifications on drinking water in Kerman in terms of various parameters, and in comparison with the national Iran standard, Environmental Protection Agency (EPA), and WHO guidelines
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All parameters of drinking water in Kerman were in the range of Iran’s national standard, and of EPA and WHO guidelines, and there is no need for the use of household water treatment systems.

Discussion

The concentration of ions of chlorine sulfate, nitrate, bicarbonate, calcium, magnesium, sodium, and total hardness had decreased considerably in output treatment systems. But the concentration of output nitrite increased with a significant difference (p > 0.05). Since the amount of nitrite in input raw water was less than the allowed limit, increasing the amount of nitrite in the output of these devices is not justified unless one assumes that these devices are not useful to remove nitrite. Also in primary tests, it was determined that free residual chlorine in drinking water in Kerman is in the range of acceptable drinking water standards.

Rajaei et al. (2013) in a study done during 2011–2012 in Iran (Arak) and Sadigh et al. (2015) in a study done during 2013 in Iran (Ardebil) showed that the concentration of nitrite ions in output of household water treatment systems significantly increased, which corresponds with the results of this study. Thus, it can be concluded that household water treatment systems examined do not have the necessary efficiency in removing nitrite. So, in cases when there is a risk of fecal contamination caused by the presence of nitrite, in the knowledge that the device cannot remove this, extra care should be taken. Also, the removal of some minerals creates a disturbance in the ion balance, and may cause an undesirable bitter taste and odor of output water from these devices (Sasidhar and Kumar 2008; Sauvant and Pepin 2002; Savari et al. 2008).

In household water treatment systems, the tested efficiency for the removal of sodium ions was 80.76%, which indicates a high efficiency of these devices to remove sodium from Kerman water. Reduction of this element is useful for patients with renal disease (WHO 2006). Sadigh et al. (2015) in a study done in 2013 in Iran (Ardebil) showed that the concentration of sodium ions of home water treatment systems’ output water was reduced significantly, which corresponds to the results of this study. Household water treatment systems tested for removing chloride ions showed an efficiency of 61.20%. The removal of chloride ions in an active carbon black filter purification device caused growth of bacteria in other parts of the water purification device. Household water treatment systems tested efficiency in the removal of nitrate at 83.66%.

Due to the negative health effects of nitrate ions, which are suspected to be carcinogenic (Gilchrist et al. 2010; Gangolli et al. 1994; Manassaram et al. 2006), and to avoid the potential effects of nitrate ions, such as nitrosamine, only where the amount of nitrate from drinking water is more than the limit mentioned in Iran’s drinking water standards, EPA, and WHO guidelines, was using water treatment systems recommended (EPA 2004; ISIRI 2009; WHO 2006). Miranzadeh and Rabbani (2010) in a study done in 2008 in Iran (Kashan) reported that the nitrate removal efficiency of water treatment systems was 60.50%, and also Tavangar et al. (2014) in Iran (Bojnord) reported that the nitrate removal efficiency of water treatment systems was 65.50%, which corresponds to the results of this study.

Household water treatment systems tested efficiency in the removal of sulfate ions at 84%. Household water treatment systems tested efficiency in removing magnesium ions at 97.87%. Sadigh and colleagues in a study done in 2013 in Iran (Ardebil) showed that the concentration of magnesium ions of home water treatment systems’ output water was reduced significantly, which corresponds to the results of this study. A magnesium deficiency in drinking water increases the risk of cardiovascular disease and stroke (ISIRI 2009; Maier 2003; Morrisa et al. 2008; Sadigh et al. 2015; Saris et al. 2000; Hammer-Sr and Hammer-Jr 2007).

With regard to the concentration of sodium ions, chloride, nitrate, sulfate, and magnesium in drinking water from Kerman being less than the limit mentioned in Iran’s drinking water standards, and EPA and WHO guidelines, using these devices is not necessary in Kerman (EPA 2004; ISIRI 2009; WHO 2006).

The great reduction in the amount of ions of sodium, chloride, and magnesium sulfate by household water treatment systems causes other problems in drinking water. Household water treatment systems remove useful ions (calcium, sodium, potassium, etc.), which is one of the disadvantages of home water treatment devices. On the other hand, they remove other harmful ions (nitrate, nitrite, etc.). Epidemiological studies have shown that moderate-to-high water hardness can be effective in reducing the prevalence of cardiovascular disease (Monarca et al. 2006). Long-term use of treated output water from water treatment systems, because of the reduction of useful minerals in water and hardness, will cause an increased incidence of bone complications from lack of nutrients (Morrisa et al. 2008). Therefore, for the above-mentioned reasons and due to studies in Kerman and other areas, since the quality of drinking water is in accordance with the Iran, and EPA standards and WHO guidelines, the use of water treatment systems devices are not required, and are expensive and not worthwhile.

Conclusion

Due to good quality, inexpensiveness, and availability of drinking water sources in Kerman, use of household water treatment systems does not have a role in health promotion and reducing disease. In addition, use of household water treatment systems is not recommended because of their removal of useful minerals, such as calcium and magnesium. Initial system purchase price with continued filter replacement costs is prohibitive. In addition, RO filters in household water treatment systems divide water into two parts: water with low mineral concentration and water with high mineral concentration.

Water with high mineral concentration enters directly into sewage output, and can cause more water consumption by water treatment systems. So use of these devices only is recommendable in areas where the drinking water is salty and has high nitrate concentration, and their application in cases where the chemical water quality already complies with desired waste energy standards.