The publicly owned company is getting a £720m loan from the Scottish government.
Projects planned for the 2015-21 investment period include more than £280m in improvements to water mains and water treatments works across Scotland.
More than £100m will be spent on waste water tunnel in Glasgow to improve water quality in the River Clyde and reduce flooding in Mount Florida and Giffnock.
More than £60m will go on reducing the impact of discharges to the River Clyde from Daldowie and Dalmarnock wastewater treatment works.
A further £45m will be spent on approximately 400 local sewer flooding problems across the country.