Objectives To analyze reasons and suggest improvement strategies by investigating an event about drinking water carrying unpleasant smell.

Methods  A field hygiene investigation including each water supply unit was conducted on April 12, and water testing result within these days were checked, for mastering changes of water indexes, including microbial index, sensory index like turbidity and taste, and chemical indicators such as oxygen consumption, ammonia nitrogen, nitrate nitrogen. Besides, event result and historical data were compared to see the difference.

Results  There were mainly 3 kinds of result. The reservoir capacity of yuejin reservoir was insufficient, water was turbid and the mud & fishy smell was obvious. Water supply was not improved when it was transported to the transfer pump station. On another source water site yuandong, water was clear, odorless and abundant. When two water line mixed, the sensory characteristics of incoming water improved obviously. The test result of source water and incoming water conform to the Surface Water Quality Standard (GB 3838-2002) Ⅱ/Ⅲ; while result of drinking water (including finished water, terminal piped water) were not completely qualified by Standards for Drinking Water Quality (GB 5749-2006). Bad smell was obvious and oxygen consumption was higher than standard. Besides, turbidity and ammonia nitrogen approached nearly to limits. There was statistical difference between lately and historical water result of the investigated water factory.

Conclusions  The peculiar smell of water originated from the mud smell of yuejin reservoir bottom. The supplement of yuandong water plays an important role in improving water quality. The water testing result within this event reflected worse water quality than those of corresponding period previously.