Major ions in drinking and surface waters from five cities in arid and semi-arid areas, NW China: spatial occurrence, water chemistry, and potential anthropogenic inputs

A total of 161 water samples were collected from five large and medium-sized city rivers and residential tap waters, Xi'an and Yan'an in Shaanxi province, Xining in Qinghai province, Lanzhou in Gansu, and Urumqi in Xinjiang province, within arid and semi-arid area (NW China). The pH, EC parameters, and concentrations of 10 major ions (F-, Cl-, HCO3-, NO3-, SO42-, NH4+, K+, Na+, Mg2+, Ca2+) in the drinking waters (DWs) and surface waters (SWs) were analyzed to determine the ion chemistry, geochemical process, and potential anthropogenic input sources and to assess the water quality for drinking, domestic, and irrigation purposes. Durove diagrams and Gibbs diagram indicated that the ions Ca2+ and HCO3- dominant in DWs from Xi'an and Xining were of Ca2+-(HCO3- + SO42-) type, while sulfate and Na+ dominant in SWs, and Na+/K+-SO42- type was for Yan River in Yan'an and Peaceful Canal in Urumqi, their water chemistry influenced by evaporation and rock dominance, and evaporation and fractional crystallization, respectively. Meanwhile, Na+/K+/Ca2+-HCO3-/SO42- type dominated in Huang River in Xining and Yellow River in Lanzhou, which dominated by rock weathering. The quality assessments showed that in general the drinking waters were suitable for domestic purposes. However, the high values of NO3- at some sites influenced by agricultural and industrial inputs made it unsafe for drinking and demand detailed regional drinking water investigations. The assessment of SWs showed that the waters from Yan River in Yan'an and Yellow River in Lanzhou and Huang River in Xining would be used for irrigation. However, high values of SAR, Na%, RSC, and EC at sites in Peaceful Canal restricted suitability for irrigation, and not recommended for drinking water sources. It was noted that for the sustainable development of surface water, a reduction of discharge water from human activities and/or an increase in the fresh water inflow to the surface were needed.