Groundwater quality assessment for drinking and irrigation: A case study in the Cauvery River Basin (CRB) of Tiruchirappalli District, Tamil Nadu, India Open Access

Water is an essential natural resource, with the primary forms of surface runoff, including rivers, streams, ponds, and canals, and groundwater entering the earth. Globally, most inhabitants depend on groundwater for drinking and domestic, agricultural, and industrial activities. In recent decades, groundwater levels have continuously been depleted due to many natural phenomena, such as increasing temperatures, low precipitation due to climate change, and substantial anthropogenic inputs affecting groundwater quality and quantity. Overextraction and groundwater consumption in many regions raise the alarm about the considerable vulnerability level and induce various waterborne diseases (Ramesh & Elango 2012; Snousy et al. 2021). In India, many states are facing the need to supply portable drinking water amenities due to population pressure, increasing living standards, domestic sewage, municipal sewers (Vetrimurugan et al. 2013), and greater-than-before industrial activities with their toxic and non-toxic effluents (Selvakumar et al. 2017; Adimalla & Wu 2019; Karunanidhi et al. 2020a). In addition, excessive usage of fertilizers and pesticides in lawns, farms, and croplands leads to soil contamination (Gautam et al. 2015), surface water contamination (Gupta et al. 2009; Janardhana Raju et al. 2011; Shankar et al. 2011), and infiltrated groundwater (Keesari et al. 2016). Both natural and anthropogenic actions enormously change the surface and groundwater chemistry (Hussainzadeh et al. 2023). The quality and quantity of groundwater commonly depend upon its chemical constituents, chiefly affected by the natural geological formations and anthropogenic activities in the surrounding regions (Shukla & Saxena 2021). Groundwater quality information systems are being developed in advanced countries to manage freshwater resources from a point or non-point source of pollution. India has been partially successful in meeting water requirements for different uses. However, preserving the quality and sustainability of freshwater resources are significant challenges. Recent studies have evaluated groundwater suitability for drinking and agricultural purposes in various regions. Benyoussef et al. (2024) assessed groundwater in North Morocco using a Geographic Information System (GIS) and multivariate statistical techniques. Their findings revealed that anthropogenic activities significantly contribute to elevated total dissolved solids (TDS) and other ions, with nitrate identified as the major pollutant in coastal areas. Imran et al. (2023) conducted a study in Pakistan's Hangu District, concluding that 92% of the groundwater samples were classified as excellent to good for drinking and agriculture, while others were unsuitable due to contamination from natural and man-made sources. In Nigeria, Nwankwoala et al. (2023) assessed the suitability of groundwater for irrigation in Rivers State, highlighting that some samples had high magnesium ratios, which could negatively affect plant growth and soil fertility. These studies emphasize the importance of understanding both natural and anthropogenic factors in groundwater quality assessment for sustainable water management. The recent studies by Patel et al. (2023) and Makubura et al. (2022) illustrated the weighted arithmetic water quality index (WQI) in identifying water quality concerns and supporting sustainable water resource management. By tailoring the index parameters to local conditions, the method remains a reliable tool for assessing water quality in diverse environments and informing efforts aligned with Sustainable Development Goals (SDGs) such as SDG 6 (Clean Water and Sanitation) and SDG 3 (Good Health and Well-being).

In recent decades, in India, attention has been drawn to studying groundwater contamination, suitability for drinking, and effect on human health (Magesh et al. 2013; Kumar et al. 2014; Selvam et al. 2017; Adimalla & Li 2019; Subba Rao et al. 2019; Karunanidhi et al. 2020b; Panneerselvam et al. 2020; Sundriyal et al. 2021; Sellamuthu et al. 2022; Girija et al. 2024). For example, research by Shukla et al. (2023) reported a critical need for intervention to espouse suitable health risk measures to decrease exposure to nitrate-contaminated groundwater. Karunanidhi et al. (2022) revealed that chemical and biological contaminants from household, industrial, and farming practices modify the water quality and threaten human health. Similarly, Ravikumar et al. (2024) examined groundwater in the Pandameru River Basin, Andhra Pradesh, and found that most samples were within permissible limits for both drinking and agriculture. However, a few samples exceeded drinking water standards due to contaminants from human activities.

The Cauvery River plays a vital role in recharging the groundwater level and supports many of the inhabitants in southern India. In Tiruchirappalli District, a few researchers attempted a different study related to groundwater quality, suitability, and contamination factors in different regions. Jameel & Hussain (2011) reported that there was no appropriate management and development for the clearance of municipal sewage in Tiruchirappalli city, and it induced the deterioration of groundwater quality. Gajendran & Jesumi (2013) revealed that groundwater in some parts of the Cauvery River Basin needs some treatment before drinking and to be protected from the risks of pollution. Rakesh & Ravichandran (2021) have conducted a seasonal variation study on water quality using multivariate techniques, and they concluded that sewage and agricultural return flow are the main reasons for contamination. The present study area, the Cauvery River Basin within Tiruchirappalli District, is one of the most crucial, cental parts of Tamil Nadu and has diverse fields of agricultural productivity and industrial activities, such as electronic equipment and glass product manufacturing, high-pressure boiler manufacturing, gem cutting, distilleries, chemicals manufacturing, korai mat weaving, and steel and cement manufacturing industries. These manufacturing effluents can discharge harmful chemicals with waste disposal into rivers and streams, and lastly, they can all affect surface and groundwater quality. Hence, the present study aims to assess the hydrochemical characteristics, groundwater suitability, and mechanisms governing the groundwater quality.

All ionic concentrations are in meq/L, and all the indices have been compared with different standards. Based on the analytical data, various representations were used by Aquachem Scientific v4.0, Rockware, and ArcGIS 10.3 software.

Sodium is considered an essential alkali metal group in groundwater. Sodium concentrations in the present study varied between 20.4 and 156.9 mg/L, with a mean value of 60.05 mg/L. The maximum value of sodium reported (Figure 4) in the sampling stations of 25, 26, 13–17 can result from natural sources, including a high rate of evaporation due to climate change with low rainfall and high temperature, weathering of top soils and the interaction between subsurface lithological formation and water, and anthropogenic inputs such as population growth, urban activities, municipal landfill leachates, improper domestic sewage, industrial discharges, and agricultural runoffs. Potassium is also one of the important alkali metals and the most common dissolved constituent in the groundwater system. The concentration of K⁺ in the groundwater samples ranges from 4.35 to 33.92 mg/L, with an average of 13.06 mg/L. Around 45% of groundwater samples exceed the maximum acceptable limits of potassium recommended by the WHO (2017). The higher values of potassium in groundwater in the present study region (Figure 4) can be sourced from the chemical weathering of silicate minerals, especially clay minerals, trapped from past geological times, and anthropogenic influences such as municipal wastewater effluents and overuse of chemical fertilizers.

Nitrate concentrations in the study area range from 8.01 to 71.93 mg/L, with an average level of 34.17 mg/L. According to the WHO and BIS standards, the maximum permissible nitrate concentration in drinking water is 45 mg/L; however, 16 groundwater samples in this area exceed this limit, rendering them unsuitable for drinking (Figure 5d). Elevated nitrate levels in groundwater pose a significant threat to water quality and public health, particularly in regions with intensive agricultural and industrial activities. While nitrate is a vital nutrient that supports primary production and biodiversity in freshwater ecosystems, in high concentrations in drinking water it can have adverse health effects, including respiratory, reproductive, thyroid, and kidney complications. Addressing this challenge aligns with the SDGs related to Clean Water and Sanitation (SDG 6) and Good Health and Well-Being (SDG 3). Reducing nitrate contamination in groundwater through these SDGs involves promoting sustainable agricultural practices, regulating industrial discharges, and implementing efficient wastewater management systems. These actions will help safeguard groundwater quality and protect community health (WHO 2017). In the study area, silica values ranged from 3.87 to 9.85 mg/L with an average of 4.79 mg/L. The high values of silica concentration were recorded in the NW part of the study area (Figure 5e) due to the weathering of silicate minerals and recharge mechanisms from soils and different sediments. Fluoride is also one of the significant threats to portable water and can cause different diseases in children and adults. Worldwide, fluoride is considered one of the important toxicological environmental hazards. In the present study region, the maximum level of fluoride is 6.09 mg/L, the minimum is 3.24 mg/L, and the average is 3.24 mg/L. The higher concentrations recorded at stations 6 and 19 (Figure 5f) are due to the subsurface lithological characteristics.

The Na% values range from 7.26 to 63.52, averaging 18.35. Based on the classification of Wilcox (1955), 89% belong to the excellent to good category, and 11% are found to be in the permissible category (Table 3). However, Na% vs. EC plot reveals that almost 95% of the samples fall in the good to permissible level (Figure 7b). Only 5% appear to be in the excellent to good categories for irrigational uses. Plant growth is stunted when high-sodium water is used for irrigation. When sodium reacts with soil, it decreases its permeability. PI values indicate that all groundwater samples in the study area are in suitable condition except one sample. Apart from Na%, EC, and PI, the magnesium content of groundwater is also one of the most important qualitative criteria in determining irrigation water quality. The magnesium hazard (MH) values ranged from 8.08 to 59.65, averaging 45.59. Based on the classification of Paliwal (1972), 93% of the samples were suitable, and 7% indicated unsuitability for irrigation. The concentration of bicarbonate and carbonate in groundwater influences its suitability for irrigation. One of the empirical approaches presumes that all Ca²⁺ and Mg²⁺ precipitate as carbonate. RSBC value of less than 1.25 meq/l is considered safe for irrigation by the US Salinity Laboratory. A value of 1.26–2.50 meq/l indicates marginal quality, while a value greater than 2.5 meq/l indicates unsuitability for irrigation. The RSBC values reveal that the groundwater samples in the study area are considered suitable for marginal irrigational purposes.

A Gibbs plot (1970) is essential and widely applied to the studies of groundwater quality for evaluating the natural mechanisms controlling the groundwater chemistry based on the relationship between three distinct properties, such as aquifer lithology (rock dominance), intensity of precipitation (rainfall dominance), and evaporation dominance. The major cations except Mg²⁺ vs. TDS plot (Figure 8b) suggested that rock–water interaction is the main mechanism governing the groundwater quality due to the leaching and weathering of parent rocks, dissolution of carbonates, and chemical weathering of silicate minerals. However, few samples were plotted outside, suggesting that some other processes of anthropogenic inputs are also noticeable factors controlling the groundwater quality. These samples are mostly located in and around the urban part of Tiruchirappalli town. Conversely, the Cl⁻ and vs. TDS plots also recommended that rock dominance is the main factor in controlling the groundwater chemistry; however, several samples demonstrated a gradually rising tendency toward the evaporation dominance field. This is expected owing to the local semi-arid environmental climate conditions with low rainfall and extensive evaporation.

The comprehensive analysis of groundwater samples conducted in the study area provided valuable insights into their physicochemical quality, enabling the assessment of their suitability for drinking and irrigation utilities. The findings indicate the samples belong to slightly alkaline and fresh to moderately fresh categories. The higher values of BOD and COD were recorded near the densely populated urban areas due to the domestic and hospital effluents, improper small-scale industrial wastes, and agricultural runoff, which also affect the groundwater quality in the highly irrigated areas. The result of physicochemical parameters revealed that most parameters are within the maximum permissible limits for drinking in accordance with national and global standards. However, high values of TH, salinity, chloride, and nitrate concentrations moderately affect the groundwater quality and make it unfit for drinking. Furthermore, different irrigation water quality indices, such as USSL and Wilcox plots, suggest that all groundwater samples are suitable for irrigation under normal conditions. The DWQI map also indicates that around 35% of the samples are in moderate quality conditions, mainly near the river channel of urban and rural areas, which indicates they are nearly in poor condition, almost unsuitable for drinking, and need to use further treatment techniques such as filtration, softening, disinfection, removal of micro contaminants, biological tricking filters, biologically activated carbon, membrane bioreactors, and different oxidation methods. The research identified that the present study regions, particularly in the urban and densely populated zones, face groundwater quality problems due to overexploitation and contamination with improper groundwater usage and unawareness of water treatment technologies. Therefore, the research recommends that urban areas and highly densely populated regions need to use wastewater treatment, particularly graywater technologies from different industries, hospitals, town halls, academic institutions, and others; the treated wastewater may be used for different agricultural purposes or as artificial recharge to augment groundwater supplies. In addition, it is crucial to promote awareness and education on water conservation and treatment, strengthen the monitoring and regulation of groundwater quality, and encourage sustainable agricultural practices. By implementing these recommendations, urban and densely populated areas can effectively address groundwater contamination, leading to improved water quality and sustainability in alignment with the SDGs, tailoring index parameters to local conditions and implementing sustainable practices such as promoting clean agriculture, regulating industrial discharges, and efficient wastewater management support SDGs 6 and 3, ensuring reliable water quality assessments and safeguarding public health.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.