In this paper, the relationship between the ultra large scale integrated circuits (ULSI) and high purity water and the demands for water quality are described.Several key new techniques of high purity water fabrication are studied. A method for improving the quality of high purity water is proposed, which can effectively decrease the concentrations of total organic carbon (TOC), bacteria and bacterial endotoxins and dissolved oxygen.The contamination of high purity water caused by various pipe materials is described.Some data and examples of author´s experiments are also included.