Section 19. A town, by a two thirds vote at an annual town meeting, or a city, by a two thirds vote of the city council, may determine to take or purchase land within its limits, which shall be a public domain, and any appropriate money and accept gifts of money and land therefor. Such public domain shall be devoted to the culture of forest trees, or to the preservation of the water supply of such city or town, and the title thereto shall vest in the city or town in which it lies, except that cities or towns owning land within the territorial limits of other cities and towns for water supply purposes may, as herein provided, convert such land into a public domain and retain the title thereto.