The company said that it is “looking at various options for the plant” and that environmental screening assessments are being carried out.
The desalination plant, which could provide up to four million gallons of water a day during times of low rainfall, is one of a number of options being considered by Southern Water as part of its water resources management plan.
Other options the company is looking at to help secure a reliable and sustainable future water supply include leakage reduction and water efficiency projects.
A Southern Water spokesman said: “Our water resources plans look forward 25 years and are reviewed every five years.
“Currently, a desalination plant is being considered for construction in Southampton by 2028 but comprehensive planning with the regulators, local authorities and environmental and community groups would be required if it was to be pursued.”
He added: “The desalination option which we have outlined would run alongside other regular resources and would only typically be used during periods of drought.”