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Intense treatment of feed water solves high demands on a demineralized water quality in the processes involving hot water/steam boilers. There are various demands on water quality parameters — its hardness, alkalinity, pH value, carbon dioxide and oxygen content, etc. — according to the type of boiler and its working pressure. Collectively, efficient demineralization and/or softening are always inevitable. Every desalination water treatment unit consists of a standard pre-treatment part and a demineralization part. Arrangement of the pre-treatment part depends on the kind of water source (well, surface, or tap water) and its individual analysis. This part of a water treatment unit is essential to protect the plant. Thereafter, the demineralization part of a water treatment unit is chosen and designed to meet product water quality demands. There are two basic methods used for brackish water desalination in the Czech Republic: reverse osmosis and ion exchangers. An application is presented of the Mega Company’s reverse osmosis units in the area of water treatment for boilers. It describes some installations and their properties — source water quality, pre-treatment techniques, and product quality. A brief comparison of the reverse osmosis process and ion exchangers is also presented.

RO is very promising technology in the preparation of water for boilers. Its application allows reduction of operating costs and the introduction of a higher level of automation of the water treatment process. It also improves ecological indices of power plants by reducing the amount and salinity of wastewaters. RO, followed by IE, can be used to prepare completely mineralfree water. When the decision between RO and IE for demineralization of water is made, then it is necessary to consider the capacity of the plant, feed water salinity and requirements of product quality. When the feed water has medium or high mineralization and the capacity of the water treatment plant is planned to be large, then it is advantageous to install RO technology. When the feed water has low mineralization, the capacity of the plant is small and product water does not need to have low TDS and conductivity, it is advantageous to install IE softening. IE demineralization is not good in any case due to the high consumption of regeneration chemicals and production of great volumes of waste water from regeneration. The future of water demineralization probably belongs to combination of RO and EDI where the chemical cost and production of wastewater are lowered to a minimum. EDI, which combines the advantages of electrodialysis and IE resins, can, in combination with RO, produce ultra-pure water of very high quality.