Bill Viola(1951-) has dealt with the most underlying problems facing human beings-life, death and existence using video as the medium, and Viola tries to find a solution to these problems in nature. In the 1970s when Viola was in full activity, Westerners came to have interest in diverse religions, such as Zen Buddhism in Japan, Taoism and philosophy. In such a social atmosphere, Viola also became interested in the Eastern religions which are in pursuit of the harmony between nature and human beings, thus reflecting this in his works. In other words, Viola, in his works, handles the representative substance elements- ‘water, fire' as main subject matter in an effort to explore the human existence in nature. The ‘water, fire' have frequently come on in myths, religions, history and cultures as the underlying elements forming the human world since ancient times regardless of the East and West. Particularly, Gaston Bachelard(1884-1962) can be pointed out as a representative philosopher among the philosophers who systematized the individual characteristics of water, fire' more concretely by applying them to the human spirit. Bachelard, in the same way as Viola, thinks that human existence bases the source of its root on nature as a human is a part of nature, and tries to look for the source of human existence in the circulation system of the natural elements-‘water, fire' Further, Bachelard applies ‘water, fire' to the human psyche and thinks that should these natural elements be born as a work in communion with an artist's imaginative action, the work would have the strength to communicate feelings to people beyond regions and the ages. Accordingly, this study is aimed at looking into what symbols and meanings such elements manifested in Viola's work have by bringing forth a question about Viola's steady work using the natural elements, ‘water, fire' as subject matter on the basis of Bachelard's argument. Viola is showing the process in which a human is endlessly linked to new creation in the natural circulation system where life and death coexist through ‛water’ and ‘fire’ among natural elements. In other words, Viola is dealing with the source of human existence using the dramatic, restrained image and the natural elements ‘water, fire' discovered in the image. Accordingly, the work of Viola, which throws a basic, intrinsic question, is inducing a variety of audiences' participation away from the boundaries between the East and West and beyond the ages, and suggesting the need to explore the matter of human existence through nature.

Presently, aquatic plants are used for the water purification in inland water. This study was carried out to investigate the water purification effect of aquatic plants, Oenanthe javanica and Typha angustata. The experiment was conducted in outdoor flowing water was conducted for ten days. Water quality was measured in terms of water temperature, COD(chemical oxygen demand), SS(suspended solids), Total N, Total P. The results of field experimentation showed that hydraulic retention time was the earliest in July and August 2003, and there were not any particular changes of monthly water temperature in inflow water and outflow water. As we look at the changes taken place in inflow water and outflow water throughout the whole experiment period, the change of water quality in summer was salient, especially SS removal ratio showed distinguished change as 25%, when the pebble filter and aquatic were attached to it. The removal rate of COD, total N total P were 14.7%, 8% and 9%, respectively. In relating the length of water extension to the change in water quality, the water quality tended to get lower generally in proportion to hydraulic retention time.