Elevated and variable groundwater iron in rural northwestern Bangladesh

Over the past 30 years, tubewells have become a ubiquitous source of potable groundwater in South Asia. Considered safer than surface water, groundwater naturally contains minerals that may impact human health; however, few data exist on tubewell water mineral content or its association with human nutritional or health conditions. We surveyed iron concentration in tubewell water across a 435 km², contiguous, rural area in northwestern Bangladesh to map and quantify levels of iron in drinking water. One tubewell was randomly sampled from each of 948 adjacent grid cells 675 m² in size. Water sampling was standardized and iron concentration measured using a field-based colorimetric kit. The median (interquartile range) concentration of iron in tubewell water was 7.6 (1.6, 17.6) mgl^-1. There was high geographic variation (range of 0-46.5 mgl^-1), and iron in only 3% of surveyed tubewells fell below the WHO aesthetic cut-off of 0.3 mgl^-1 suggesting elevated levels of iron throughout the area. Villagers accurately perceived groundwater iron concentration, based on a 4-point ('none', 'a little', 'medium', 'a lot') scale ( p < 0.001). Water source iron content can be readily quantified in population settings offering the potential to evaluate the health relevance of groundwater iron exposure in rural communities.