In the fields of electronics, semiconductors and electrocoating industries, the requirements for water may include conductivity in addition to suspended solids and turbidity. The traditional process is to use steaming, anion, cationic resin exchange process to remove water ions, reduce the electrical conductivity. With the popularization and application of reverse osmosis(RO) membrane technology, the membrane method reduces the electrical conductivity, and the preparation of pure water gradually replaces the traditional occupy the mainstream. Using RO technology, the process is more simple, the equipment is more compact, the water quality is higher and the water quality is more stable. In the process of preparing high pure water, two stage reverse osmosis, EDI electric desalination and carbon dioxide removal can also be used.