Abstract
The aim of the study was to determine changes of daily amount of sewage inflowing into a wastewater treatment plant in Nowy Sącz in the years 2008-2014. To this end, the data in the form of time series corresponding to the investigated multi-year period were analysed. Daily volume of sewage for annual periods was forecast using a seasonal method of Holt and Winters based on the exponential smoothing algorithms. The model fit to actual daily amount of sewage for 2014 was assessed using linear regression. The results of fit for the additive Holt-Winters model confirmed the usefulness of this tool for forecasting the amount of sewage inflowing into the wastewater treatment plant.