The DCDW with poor iodine may occur in the oxidizing(intake) area, and the DCDW with rich fluorine may occur in reducing (discharge) area, and the Keshan disease of DCDW may occur in a damp area where the FUW is rich in H 2S gas and organic matter.

• 在氧化带（补给区）易发生碘缺乏病，在还原带（排泄区）易发生氟中毒病，在富有机质和H2S的潮湿地带易发生克山病。