Based on the water quality monitoring data of drinking water sources developed from August 2008 to December 2009 on the Zhoushan Island and Putuoshan Island in Zhejiang Province, the characteristics and causes of water pollution by iron and manganese were discussed. The results indicated that iron and the manganese concentrations in reservoirs and rivers of Zhoushan were high from June to November. Iron and manganese showed a typical vertical distribution in some reservoirs in summer. Iron and manganese concentrations in the continent raw water diverted from the Yaojiang River to the Zhoushan Island were high all the year round.