CEDEX (Centro de Estudios y Experimentacion de Obras Publicas) and EMALSA (Empresa Mixta de Aguas de Las Palmas, S.A.) had been performing experimental tests for seawater desalination at Las Palmas, Gran Canaria Is., Spain, using a TOYOBO hollow-fiber membrane. A Hollosep HM10255FI module made by TOYOBO is used in the largest desalination plants around the world, especially in the Middle East. CEDEX and EMALSA confirm that the Hollosep module can produce stable water production and high-quality water for long-term operation without any chemical cleanings during 4600 h operation thanks to the its high chlorine resistance and anti-biofouling tolerance.