The earliest known of the cascade type of aerator, working in series, was put into use in 1848 by the Gorbals Gravitation Water Co. to supply water to a district afterwards annexed to Glasgow, Scotland. Water from a large settling reservoir cascaded into a basin and from it into the first of three filters, arranged in steps. Similarly there was a cascade between the first and second filters, the second and third filters and the third and last filter and a clear water reservoir.