Section 8B. The following words and phrases, as used in this section and sections eight C and eight D, shall have the following meanings:--
''Commission'', the water resources commission.
''Interbasin transfer'', any transfer of the surface and groundwaters, including wastewater, of the commonwealth outside a river basin. If a city or town partially situated within a river basin takes waters from that basin, extension of water services to a portion of the same city or town outside the basin shall not be deemed an interbasin transfer of water.
''Insignificant increase'', an increase insufficient to invoke the provisions of section eight C and eight D as determined by the commission; provided, however, that in no event shall an increase over one million gallons per day be deemed insignificant.
''River basin'', a geographic area within the commonwealth determined by a body of water and its surrounding drainage area as delineated by the commission.