In an ultra pure water (UPW) production system which can satisfy the water qualities for 4 megabit DRAM, the changes in water qualities from a tap water (58.4 mg/dm3 as CaCO3 hardness) as a raw water to UPW were followed from the view of the micro-structure and microdynamic behavior of water molecules with increasing of the water purity by a complex permittivity and 17O-NMR measurements, as well as measurements of resistivity, density, and so on. The dielectric relaxation time and spin-lattice relaxation time of 17O nuclei related to the microdynamic behavior of water molecules indicated a trace change between the tap water and UPW. However, the dielectric parameter α which characterizes a symmetric distribution of relaxation times was gradually lowered with increasing of the water purity. The relationship between the half-width of 17O magnetic resonance and pH gave the rate constants for the prototropic charge migration in water. The difference of α and density between the tap water and UPW became a measure of water purity.

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