The first Module of Guilan water treatment plant has been founded in 1991, in north of Iran by the sea, with nominal capacity of 3 m³/s.After 17 years in 2018, another module is signed to be installed beside the first running module to increase the capacity of WTP. Regarding the size of the project and strategic usage of WTP in IRAN, big companies invited to the project. The Joint venture of Tana Energy and Zolal Co., with IRANAB as consulting company took the MC of the whole project. Detail design, Material Procurement, programming and startup after commissioning the second module has been outsourced to ICP.Besides providing DCS for the newly expanded module, ICP is contracted to replace existing control system of in use module, which now is almost 20 years old and from Schneider technology.Our proposed solution for main DCS of plant is based on Symphony controllers, a well-known series of ABB technology.Upon Request Settling pools of plant and filtration facilities will be monitored separately and through ABB- AC500 series. The localized PLCs are connected and transferring data through planned network to main DCS. Integrated monitoring system to having detailed preview of the site will give the operators an exact information and commanding options, whenever has been required.Providing the whole control systems of plant is in our scope of work, which consisting 5 PLC for filtration utilities, 8 other PLC panel and 16 panels for remote I/Os. The number of I/O s in this proejcts is estimated around 4200 signals, which are transferring data/commands all over plant using fiber optic infra structure.