Spatial variations in total aluminum concentrations in drinking water supplies studied by geographic information system (GIS) methods

Aluminum sulfate (alum) is routinely added in many water treatment systems as a coagulant. Some amount of aluminum may persist in the filtered water designated for human consumption. However, there are no reliable data to predict the magnitude of residual concentrations that would reach consumers’ taps. Studies in the United States, Canada, Europe, and Japan associated aluminum in tap water with various health problems, most notably, neuro-skeletal disorders and cognitive impairments. Whether or not aluminum in the drinking water is, indeed, a risk factor for these diseases has not been resolved conclusively. However, evidence has accumulated to suggest that it might be prudent to minimize residual aluminum in drinking water supplies. Harris County, Texas, by virtue of its multiple water supply sources and treatment methods, provides a unique opportunity to study spatial variations in concentrations of aluminum in the tap water within a defined geographic location. Statistical analysis of sampling results, coupled with GIS mapping, showed a range of variations, from none detected to as much as 530 μg/l of total aluminum in tap water. Peak concentrations were associated with source water treated with alum and were 2.5 times in excess of 200 μg/l currently recommended for public drinking water supplies. Median concentrations in the alum-treated water were up to five times greater than in raw water, regardless of its origin (surface or ground), and greater than in the water treated with an alternative coagulant (ferric chloride). Our findings show that options exist to minimize residual aluminum and these options need to be explored.