Water quality assessment of an unusual ritual well in Bangladesh and impact of mass bathing on this quality

- Ritual well water was analyzed in three seasons and during mass bathing.
- Water fulfilled the standards for bathing water in all seasons.
- Physicochemical parameters fluctuated unusually during mass bathing.
- Microbial indicator concentration increased after the mass bathing.
- Some parameters and indicators showed significant relationship among them.

A sacred ritual well with continuously discharging of methane gas through its water body was studied for physicochemical and microbiological quality in three seasons and during ritual mass bathing. Most of the physicochemical parameters showed significant seasonal variations (P < 0.05) and a sharp fluctuation during mass bathing. Dissolved oxygen (DO) was found negatively correlated with temperature (r = − 0.384, P < 0.05), biochemical oxygen demand (BOD) (r = − 0.58, P < 0.001) and ammonia (r = − 0.738, P < 0.001), while BOD showed positive correlation with chemical oxygen demand (COD) (r = 0.762, P < 0.001) and ammonia (r = 0.83, P < 0.001). Simple regression analysis also yielded significant linear relationship in DO vs. temperature (r2 = 0.147, P < 0.05), DO vs. ammonia (r2 = 0.544, P < 0.001) and BOD vs. DO (r2 = 0.336, P < 0.001). A total of eight microbial indicators were studied and found that all of them increased unusually during mass bathing comparing with their respective seasonal values. Total coliforms (TC) were found positively correlated with fecal coliforms (FC) (r = 0.971), FC with Escherichia coli (EC) (r = 0.952), EC with intestinal enterococci (IE) (r = 0.921), fecal streptococci (FS) with IE (r = 0.953) and Staphylococcus aureus (SA) with Pseudomonas aeruginosa (PA) (r = 0.946), which were significant at P < 0.001. Some regression models showed significant linear relationship at P < 0.001 with r2 value of 0.943 for FC vs. TC, 0.907 for EC vs. FC, 0.869 for FS vs. FC, 0.848 for IE vs. EC and 0.909 for IE vs. FS. The overall results found in this study revealed that well water is suitable for bathing purpose but the religious activity considerably worsen its quality.