Frank J. Horgan Filtration Plant The Frank J. Horgan Filtration Plant is located Southeast of Toronto on the shores of Lake Ontario (See map). Its purpose is to provide safe drinking water to our taps by filtering the water. The water is gathered from Lake Ontario. This plant has a production capacity of 455 million litres per day to supply the residents of Toronto with drinking water. Its average production of drinking water is 355 million litres per day. It is also the newest filtration plant in Toronto. History The Frank J. horgan Filtration Plant was built from 1974 to 1979 on property