Speaking during debate in the National Assembly on her department's 2013/14 budget on Tuesday, she said this included the cost of refurbishing the country's ageing, existing plants and treatment works.
"Capital investment in new water and sanitation infrastructure for the entire value chain … is projected to require an estimated R670-billion over the next 10 years, or an equivalent of R67-billion a year."
However, only R30-billion a year was available from current resources and government would have to look to the private sector for help.
"These investments will have to be funded from on-budget and off-budget sources through the private sector," she said.
Meanwhile, the minister assured MPs that South Africa will not run out of water in the next 100 years.
Molewa dismissed what she referred to as "the current myth" about the country running dry.
'SA will not run out of water'
"You must have heard, from one source or another, how South Africa will 'run out of water' in 2013, 2015, 2025, or 2030, depending on which news source you rely on.
"Let me assure you, as the custodian of water resources in this country, that as we enter the third decade of equity and redistribution, South Africa will not run out of water in the next 100 years."
She said this did not mean there would be no problems "regarding water resources' availability".
However, her department was confident that as a result of its planning, future programmes, and the development and management of infrastructure, it was "geared towards sustainability and a secured future in terms of security of [water] supply".
Earlier, briefing reporters at Parliament, Molewa said: "We might have water shortages if we don't do certain things, but running out of water completely is a no-no." – Sapa