The use of membrane techniques in the preparation of water supplementing cooling and water-steam cycles is becoming a standard solution. This is primarily due to the increasing requirements to reduce the salinity of discharged sewage, which in many cases eliminates the possibility of using the traditional ion exchange process. The technological and economic efficiency of membrane systems operation mainly depends on the quality of water feeding the membranes. Therefore, pre-treatment systems for water supplying membrane installations should be designed and operated in such a way as to obtain the best possible quality parameters that have a direct impact on the effectiveness and service life of the membranes. In practice, this involves removing substances from raw water that cause the so-called fouling of osmotic membranes. The most common substances of this type include organic compounds included in the so-called Natural Organic Matter (NMO) and microsuspensions and colloidal compounds. The most effective method of removing them is coagulation. However, the method of coagulation depends on the form of organic compounds and their susceptibility to sorption and precipitation. The article presents the effects of implementing the sweep coagulation process in the pre-treatment system for water supplying membrane installations in systems for preparing demineralized water and water for supplementing heating circuits in the completed facility.