The main aim of the work is to study the natural and climatic factors influence on the degree of change in waste fluid temperature in open facilities, depending on the design features of the main facilities (primary sumps, aeration tanks and secondary sumps), indicators for the sewage treatment, as well as a year seasons. It should be noted that today waste fluid temperature influence on the processes of sedimentation and biological treatment has been studied and mathematically described quite well. The high convergence of theoretical result, obtained using these mathematical models in the design with production data, has been repeatedly verified and proved. The statistical data collection on STF operating of Novosibirsk and Iskitim (Novosibirsk region) on the changes in waste fluid temperature at different stages of its purification was carried out for a long time, covering all seasons of the year. Mathematical processing of statistical data made it possible to obtain multivariate regression models that could be used to predict the actual temperature of waste fluid, depending on the operating conditions of wastewater treatment complex.