Nowadays, water supply is available in nearly 96% of Japanese homes, though an array of problems such as deterioration of raw-water quality, a shortage of water-supply engineers, increasingly obsolete water-purification plants, damage associated with chlorine-resistant bacteria, and carcinogenic substances typified by trihalomethanes have yet to be resolved. While addressing these problems and adopting simple maintenance work, modern water-purification technology is required to produce safer and cleaner drinking water. As new technology meeting these requirements, membrane filtration systems are receiving widespread attention these days. In commercializing this particular technology, however, there is a need to reduce maintenance costs such as those for cleaning membranes with chemicals, and replacing old membranes with new ones. In consideration of these requirements, we have developed a high-efficiency membrane filtration system based on a combination of pre-treatment (coagulation with ferric chloride and high flux fiber filtration) and membrane filtration. The results of long-term performance tests show that this system can remove colors and organic matters, both of which can hardly be filtered out by membranes, while carrying on steady operations without causing any clogging even at high-speed filtration.