Stable isotopes reveal the origin and vulnerability of bottled and sachet drinking waters sold in Cameroon

Urbanisation and unreliable drinking water supply have increased reliance on packaged waters in Cameroon. However, their hydrogeological origin is poorly verified. This study investigated the spatio-temporal variation, origin, recharge and vulnerability of 35 brands (114 samples) in Cameroon (2012 to 2025) using stable isotopes and major anions. The δ18O range (-5.70 ‰ to -3.34 ‰) reflected wide spatial variation, controlled by altitude, local climate and distance from the Atlantic moisture source. The δ2H/δ18O relationship revealed meteoric-recharged groundwater sourcing through springs and boreholes. Brands sourced from Mount Cameroon had the highest elevation-recharge isotope characteristics. Those in Douala showed the lowest elevation-recharge isotope signatures and higher vulnerability to contamination (elevated NO3−). Measured and labelled concentrations differed, revealing poor labelling practices. Most brands showed limited temporal isotopic variation, exhibiting stable groundwater sourcing and aquifer buffering capacity. Stable isotopes and hydrochemistry provide a tool for commercial water verification and drinking-water management in Cameroon.