The waste water treatment register of Simno komunalistas, a municipal enterprise in Alytus district, accumulates the values of the pollution indicators after treatment. The dataset includes data from 2018. The dataset includes: the name of the treatment plant, the names of the contamination indicators and the values of the indicators and the dates of the first six months when the contamination was measured. The data set is in a long format, so the data for one cleaning plant is arranged vertically.