Ross is currently executive director of markets and economics at the Office of Rail Regulation. She previously worked at Ofwat as director of markets and economics between 2008 and 2011, and has served with the Competition Commission.
She is to start induction at the water regulator as soon as possible and officially takes up the appointment on 14 October, after completing the rail regulatory review.
Ofwat chair Jonson Cox welcomed Ross, who he said would bring a “strong team focus” at a “critical time”. He added: “Cathryn’s first priorities will include refocusing the future direction and management process of Ofwat.”
Ross joins shortly before water companies submit their 2015-20 business plans for the 2014 periodic review.
She said: “I am very pleased to be returning to Ofwat at this key time. I am looking forward to working with Ofwat’s board, staff and stakeholders to ensure the success of the current periodic review and the development of a new model for water regulation.”
The Ofwat board will propose the appointment to environment secretary Owen Paterson.