Cooling water systems mainly depend on the type of water source. With the increasing use of sea water as feed the cooling water system is usually based on a closed circuit of soft cooling water and a semi-open circuit of saline cooling water, with a sea water cooling tower and sea water make-up. The soft cooling water is a treated-water closed loop – filled with demineralised water coming from a suitable polishing package - indirectly cooled by sea water by means of plate heat exchangers. Less sophisticated systems may be specified in case of different raw water source, but the double circuit, consisting in a combined open/closed system, appear to be the most cost-effective, to minimize water, power and chemical consumption, while at the same time ensuring an acceptable temperature level of the cooling water. Closed systems, in fact, allow a better control of temperature by users, a low risk of both corrosion (since recirculating water is not continuously saturated with oxygen, as in an open system) and biological fouling from slime and algae, and small makeup water requirements. Also, the risk of mechanical failure is reduced, and the working life of heat exchangers is extended, making use of high-quality water. At Energeco we provide accurate evaluation of the most suitable cooling water systems and provide basic design, detailed engineering, construction and commissioning supervision services for any possible scenario, always taking into account the environmental and safety aspects.