For the purpose of sections 249.430 to 249.660, the following definitions will apply:
(1) "Lateral sewer district" shall mean all of the area served by a lateral area;
(2) "Main sewer district" shall include all of the area in, and including the watershed, and including the area of any submain and lateral sewer districts served by the main sewer;
(3) "Submain sewer district" shall mean all of the area served by a submain sewer district and shall include the area of any lateral sewer district served by a submain sewer.