Chlorination has been believed to be the best sterilization method in water supply engineering for many years. However, the recent carcinogenic problem of trihalomethanes (THM) formed from organic compounds by chlorination requires us to assess the public health risk of THM.
The author tried an assessment of a suitable chlorination technique considering both the effects of THM and viruses on human health, using Lake Biwa as a representative example of a water resource in Japan. Statistical handling of data was revealed to be important because of the statistical nature of the data. In other words, since both concentrations are very low in tap water, we need to quantify both the effects and concentrations with probabilities.
In the first part of this paper, a statistical procedure and numerical results of the assessment of virus and THM risks are shown. In the second part some results of accuracies in virus experiments are briefly shown. These experiments concerning statistical problems are particularly important for more precise assessment of the public risk of viruses in tap water.