Laxative Effect
The laxative effect is observed only when the sulphates present in water have concentrations greater than 500 𝑝𝑝𝑚.
A moderate concentration of sulphate ions in water is harmless but excessive concentration, i.e., greater than 500 𝑝𝑝𝑚 in water causes laxative effects. Hence, underground water may have consisted of excess sulfates and thus the person felt laxative effect on drinking that water.