The paper demonstrates the possibility to apply the methods of membrane and ion-exchange division to estimate a part of monomeric-dimeric, polymeric and anionic silicon forms. The authors have studied the influence of pH solution on quantitative ratio of silicon various forms. The subsequent water filtration through the membrane with pore diameter of 0,05 μm and then through the column with anion-exchange resin АV-17-8, ОН -f was proposed for desiliconization. It was ascertained that the method of atomic-absorption spectroscopy with electrothermal atomization is preferred to be used to determine the overall concentration of silicon soluble compounds in natural waters. The comparison of the analysis results by the methods of а atomic-absorption spectroscopy and spectrophotometry allows obtaining the information on the ratio of monomeric-dimeric and polymeric silicon forms.