Chemical quality of urban and rural drinking water, in Tarapaca, northern arid area of Chile

Abstract

The population of Tarapacá, northern Chile, is supplied with drinking water of underground origin. The objective of this study was to evaluate the chemical quality of water for human consumption in nine urban and rural locations and its compliance with current norms (temperature, salinity, alkalinity, dissolved majority ions, As and B). Geochemical classifications were deduced to consider the origin and relationships between waters. Moreover, five water stability indicators were evaluated to estimate potential corrositivity (B/Cl- ratio, Cl-/SO42- ratio and Larson ratio) and calcareous inlays formation (Langelier Saturation Index and Ryzman Stability Index). The samples analyzed were determined had mild temperatures, slightly alkaline, with a wide range of values of salinity (74.7 - 1287 mg L-1). The hydrogeochemical results confirmed four water types: Na+/HCO3--Cl-SO42-, Na+/SO42-, Na+-Ca2+/SO42-, and Na+-Ca2+/Cl-SO42-. The 168 samples reached 100% of the degree of compliance of NCh409, except in the wells of Colonia Pintados, where As concentration exceeded 13 to 30 times the norm. Sulphate and B exceeded international standards. The water taste deterioration can be attributed to high concentrations of SO42-, Cl-, Ca2+, and B. Finally, water stability indexes determined the capacity for severe corrosively potential and formation of light calcareous deposits. The internal regulations of the country must harmonize and admit substances suggested by the WHO.