Low water peak single mode fiber (LWP-SMF) fabricated by PCVD based process has been described. Based on the whole process of PCVD fiber, the hydroxyl contamination and its sources are as follows: (1) raw material, such as SiCl4, GeCl4, O2, C2F6, substrate tube and jacket tube; (2) leakage of the system including PCVD and collapsar; (3) surface contamination. The latter purification of deposited glass is extremely difficult, so the most effective solution is prevention. The hydroxyl contamination prevention and elimination measures, such as purity improvement of raw material, online purification during PCVD, surface absorption reduction and dilution effect with large preform, which are the key factors for LWP-SMF fabrication by PCVD based process, are revealed. Large scale production has revealed that LWP-SMF can be fabricated by PCVD based process combined with above mentioned process innovation. PCVD LWP-SMF complies with or exceeds the ITU recommendation G.652 (C and D) and IEC 6093-2-50 type B 1.3 optical fiber specification. With further development of high purity raw material, machine-airproof improvement and larger preform (above 150mm) combined with material composition and structure optimization in optical fiber or preform, high performance PCVD LWP-SMF with lower water peak or even zero-OH performance will be achieved. Besides, other type of optical fiber with low water peak, such as G.653, G.655 and G.656, can also be made with the advanced PCVD based process.