Samples of groundwater were collected during a post-monsoon period (January) and a pre-monsoon period (May) in 2020 from 30 locations in the rapidly developing industrial and residential area of the Coimbatore region in southern India. These sampling periods coincided with times before and during the lockdown in industrial activity and reduced agricultural activity that occurred in the region due to the COVID-19 pandemic. This provided a unique opportunity to evaluate the effects of reduced anthropogenic activity on groundwater quality. Approximately 17% of the wells affected by high fluoride concentrations in the post-monsoon period returned to levels suitable for human consumption in samples collected in the pre-monsoon period. This was probably due to ion exchange processes, infiltration of rainwater during the seasonal monsoon that diluted concentrations of ions including geogenic fluoride, as well as a reduction in anthropogenic inputs during the lockdown. The total hazard index for fluoride in the post-monsoon samples calculated for children, adult women, and adult men indicated that 73%, 60%, and 50% of the groundwater samples, respectively, had fluoride levels higher than the permissible limit. In this study, nitrate pollution declined by 33.4% by the pre-monsoon period relative to the post-monsoon period. The chemical facies of groundwater reverted from the Na-HCO₃-Cl and Na–Cl to the Ca-HCO₃ type in pre-monsoon samples. Various geogenic indicators like molar ratios, inter-ionic relations along with graphical tools demonstrated that plagioclase mineral weathering, carbonate dissolution, reverse ion exchange, and anthropogenic inputs are influencing the groundwater chemistry of this region. These findings were further supported by the saturation index assessed for the post- and pre-monsoon samples. COVID-19 lockdown considerably reduced groundwater pollution by Na⁺, K⁺, Cl^–, NO_3¯, and F^– ions due to shutdown of industries and reduced agricultural activities. Further groundwater quality improvement during lockdown period there is evidence that the COVID-19 lockdown by increased HCO_3¯ ion concentration. Overall results illustrate the positive benefits to groundwater quality that could occur as a result of measures to control anthropogenic inputs of pollutants.

在 2020 年季风后时期（1 月）和季风前时期（5 月）期间，从印度南部哥印拜陀地区快速发展的工业和住宅区的 30 个地点收集了地下水样本。这些采样期与工业活动封锁之前和期间的时间相吻合，并且由于 COVID-19 大流行，该地区发生的农业活动减少。这为评估人为活动减少对地下水质量的影响提供了独特的机会。在季风后期收集的样品中，大约 17% 的受高氟化物浓度影响的水井恢复到适合人类食用的水平。这可能是由于离子交换过程，季节性季风期间雨水的渗透稀释了包括地源氟化物在内的离子浓度，以及在封锁期间人为输入的减少。为儿童、成年女性和成年男性计算的季风后样本中氟化物的总危害指数表明，分别有 73%、60% 和 50% 的地下水样本的氟化物含量高于允许限值。在这项研究中，相对于季风后时期，季风前时期的硝酸盐污染下降了 33.4%。Na-HCO恢复的地下水化学相 分别有 60% 和 50% 的地下水样品的氟化物含量高于允许限值。在这项研究中，相对于季风后时期，季风前时期的硝酸盐污染下降了 33.4%。Na-HCO恢复的地下水化学相 分别有 60% 和 50% 的地下水样品的氟化物含量高于允许限值。在这项研究中，相对于季风后时期，季风前时期的硝酸盐污染下降了 33.4%。Na-HCO恢复的地下水化学相_{季风前样品中的3} -Cl 和 Na-Cl 到 Ca-HCO ₃类型。各种地质指标，如摩尔比、离子间关系以及图形工具表明，斜长石矿物风化、碳酸盐溶解、反向离子交换和人为输入正在影响该地区的地下水化学。为季风后和季风前样本评估的饱和指数进一步支持了这些发现。COVID-19 封锁大大减少了 Na ⁺、K ⁺、Cl ^–、NO _3¯和 F ^{–对地下水的污染}由于工业停工和农业活动减少而产生的离子。封锁期间地下水质量的进一步改善有证据表明 COVID-19 封锁是通过增加 HCO _3¯离子浓度来实现的。总体结果表明，控制人为污染物输入的措施可能对地下水质量产生积极影响。