Poland's accession to the European Union contributed to the infrastructure development of the whole country. One of the elements of the modernized infrastructure is the sewage network and facilities on this network, as well as facilities for waste water treatment and disposal of sludge. A wide stream of funds flowing to the country, and consequently also to the north-eastern polish voivodeships (Podlaskie, Warmian-Masurian, Lublin), allowed modernization, organize, and sometimes to build a new sewage management of this part of the country. The main factors and parameters that allow us to evaluate the development of the sewage management in north-eastern Poland are included: percentage of population using sewage treatment plants, number of municipal sewage plants with the division of their type, number of industrial plants, number of septic tanks, amount of sewage purified in a year, amount of sludge produced in the year, design capacity of sewage treatment plant, size of plant in population equivalent (PE). From a number of investments in the field of wastewater management carried out in the discussed area in the period after Poland's accession to the European Union, 9 investments were considered the most important, 3 from each of the voivodeships.