South Staffordshire Water has unveiled plans for the 30-acre (12.2 hectares) Seedy Mill Water Treatment Works site in Hanch, Lichfield.
The scheme will see the demolition of the existing bottling plant, which opened in 2004, while a new rapid gravity filter building will be erected, along with a pumping station, new kiosks and tanks.
The works, off Lichfield Road, is the second largest water production site in the area, and has served the people of South Staffordshire since the 1950s.
A statement accompanying the plans says that "extensive rebuilding and refurbishment work" is required at Seedy Mill following an order from the Drinking Water Inspectorate (DWI).
The works form part of a 10-year-plan to revamp the site, it adds, enabling improved water quality and to ensure continued supply.
The statement says: "In response to the Drinking Water Inspectorate’s direction it is proposed to erect a rapid gravity filter building and associated structures in the vicinity of the bottling plant that is to be demolished.
"The associated structures include a motor control centre kiosk, blower kiosk, pumping station, backwash tank and washwater tank.
The pumping station and washwater tank will be predominantly below ground."
It adds: "The proposed works are required to maintain the function of the site as a water treatment works, improve the quality of water and thus enable the supply of water to be maintained to existing customers.
"The installation of the proposed plant and buildings is evidently necessary and related to the use of the application site as a water treatment works."
The statement also addresses the issue of green belt development, saying it will "not encroach into the countryside".
It says that although the site sits within Staffordshire's green belt, the proposals would have a limited impact on the 'openness' of the green belt as it has already been built on previously.
"The proposed development does not extend the built form beyond the boundaries of the operational land at Seedy Mill. In spatial terms, inevitably there would be a slightly greater impact on the openness of the site itself.
"However, given the scale and nature of the structures on site, the impact on the openness of the Green Belt is not considered to be harmful," the statement says.
A DWI report in 2018 noted that South Staffordshire Water had said there was "a significant risk of supplying water from Seedy Mill WTW that could be unwholesome".
The plans are under consideration by Lichfield District Council.