A study has been carried out in order to establish the possibility for natural water coagulation via its treatment with strong acid cation exchangers modified with FeCl3 or Al-2(SO4)(3). Various trademarks of ion exchangers have been used, such as Wofatit KPS, Wofatit KS-10, Lewatit S-100, VaWon KSM, Amberlite 200 C and Duolite C-26. It has been found that, while using modified ion exchangers the concentration of suspended solids, permanganate oxygen demand and humic acids in treated water are reduced respectively by approximately 95, 86 and 77% with FeCl3 used as modifier, and 92, 80 and 73% with Al-2 (SO4)(3) as a modifier The modified ion exchangers can be used for pretreatment of natural water needed for small water make up installations of a module principle. Different modules of these installations can be regenerated in a central station. A scheme has been proposed for natural water treatment combining the process of coagulation with modified ion exchangers and Na-Cl-ion exchange in a mixed bed filter. This can produce conditioned water suitable for thermal plants or for subsequent membrane desalting process.