Objective To test the quality of drinking water from multiple sources in Zhoushan archipelago, to evaluate the value of hybrid application of desalinated seawater and water of other sources, and to provide reference for drinking water safety.
Methods Various water samples were collected, including 270 samples of reservoir water, 222 samples of river water, and 192 samples of municipal supply water tested by Zhoushan Municipal Center for Disease Control and Prevention (2009-2011); 36 samples of water diverted from Ningbo city by Zhoushan Water Supply Company (2009-2011); and 128 samples of desalinated seawater (2009-2011) as well as 299 hybrid samples of desalinated seawater and surface water (2004-2006) by Shengsi County Center for Disease Control and Prevention. Analyses included aerobic plate count, thermotolerant coliform, boron, total hardness, and chloride in the samples of municipal supply water, desalinized seawater, and hybrid of desalinized seawater and surface water, as well as ammonia nitrogen, chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), dissolved oxygen (DO), total nitrogen, total phosphorus, permanganate index, and faecal coliform counts in water samples from reservoirs, rivers, and diverted water.
Results The reservoir water samples showed relatively high qualification rates in all indicators except total nitrogen (46.7%). The qualification rates of all indicators were relatively low in the river water samples, the levels of total nitrogen, total phosphorus and permanganate exceeded the limit of Category III water source according to the national classification of surface water environmental functions, and the levels of some other indicators including ammonia and total nitrogen were beyond the limit of Category V. Only 41.7% and 8.3% of diversion water samples were within the limits of ammonia nitrogen and total nitrogen respectively, and some other indicators including ammonia and total nitrogen went beyond the limit of Category V water source. In the desalinated seawater samples, barely 21.6% were qualified in the boron indicator, but the rates were high in the rest indicators. As to the samples from municipal supply water and the hybrid of desalinated water and surface water, the qualification rates of all indicators were relatively high.
Conclusion The qualification rates of 8 pollution indicators detected are relatively low and many exceed the limit of national Category III water source, some of them go beyond the limit of Category V, in the source water of Zhoushan archipelago. There are potential risks in the hybrid application of desalinated seawater and mainland diversion water.
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