Data regarding population connected to wastewater treatment plants are data based on estimations and come from OS-5 report (Report on municipal and rural wastewater treatment plants). An estimate of population connected to wastewater treatment plants by a given area of city/gmina is provided e.g. on the basis of wastewater disposal and treatment contracts, the number of sewage connections, data on population connected to wastewater treatment plants obtained from housing cooperatives or from design data of wastewater treatment plants. The estimated number of population connected to wastewater treatment plants cannot exceed the number of population residing in a given gmina (as of 31 December of a reporting period). OS-5 report does not include information on population temporarily staying in a given gmina (tourist purposes) or employees generating municipal waste that is disposed to a wastewater treatment plant by their work establishment. The report does not contain data on population whose wastewater has been transported to the wastewater treatment plant or a cast station by sewage disposal vehicles (wastewater stored temporarily in septic tanks) either. Indicators relating to the number and structure of the population (gender, age group) since 2010 have been recalculated in accordance with the balance sheet prepared on the basis of the results of the National Census 2011. Indicators relating to the number and structure of the population (gender, age group) since 2020 have been recalculated in accordance with the balance sheet prepared on the basis of the results of the National Census 2021.