Objective To investigate the levels of 9 metals/metalloids in source water and finished water of Guangzhou waterplants.

Methods  The levels of cadmium, manganese, lead, arsenic, iron, copper, selenium, zinc, and chromium were determined for the source water and finished water of Guangzhou waterplants from 2003 to 2019 according to the Sanitary Standards for Drinking Water (2001) before 2006 and the Standard Examination Methods for Drinking Water (GB/T 5750-2006) after 2006. The Environmental Quality Standards for Surface Water (GB 3838-2002) (Class Ⅲ) and the Standards for Drinking Water Quality (GB 5749-2006) were used to evaluate the 9 metals/metalloids in source water and finished water, respectively. The chi-square test was used to analyze the excess metals/metalloids in source water and finished water in different water systems and quarters.

Results There were excess iron, manganese, and lead in the source water of Guangzhou waterplants, with qualified rates of 40.66% (209/514), 64.59% (322/514), and 98.83% (508/514), respectively, and there was a tendency of increase in the qualified rates of iron and manganese (χ² = 18.30 and 131.54, P < 0.01). There were excess manganese and iron in finished water, with qualified rates of 93.97% (483/514) and 99.81% (513/514), respectively, and the qualified rates of iron, manganese, and lead in finished water were significantly higher than those in source water (χ² were 430.01, 135.02, and 6.04, respectively, P < 0.05). There were significant differences in the qualified rates of iron and manganese between the source water from different water systems, and the qualified rates of iron (20.14%) and manganese (12.50%) in the Pearl River were lower than those in other water systems. In addition, there were also significant differences in the qualified rates of iron and lead between different quarters; the qualified rates of iron in the first and fourth quarters (53.44% and 50.40%, respectively) were higher than those in the second and third quarters (27.27% and 31.75%, respectively), and excess lead was observed in some water samples of source water in the second and third quarters.

Conclusion Excess iron, manganese, and lead are observed in source water of Guangzhou waterplants, and excess iron and manganese are observed in finished water. Source water from the Pearl River has the lowest qualified rates of iron and manganese. Iron, manganese and lead should be focused on in the future, and monitoring indice and frequency should be timely adjusted based on the real-time monitoring data of source water and finished water.