The first stage involves appointing two partners - one for water and one for waste water - to deliver a programme of upgrades, maintenance and new infrastructure assets between 2015 and 2021.
The utility has appointed Caledonia Water Alliance, a partnership of Morrison Utility Services and Aecom, for its £360m water infrastructure programme, while BBV Alliance, a partnership of US-based Black and Veatch and Byzak, part of the Amey group, will deliver the £340m waste water work.
Morrison is the only Scottish-based business, while US consultancy Aecom is the only newcomer to Scottish Water infrastructure contracts.
Geoff Aitkenhead, Scottish Water's director of asset management, said: "We had a large number of interested parties keen to work with Scottish Water on our next investment programme.
"We are building strong relationships with our alliance partners which I believe will last beyond 2021."
Mr Aitkenhead added the alliances would "help us deliver the benefits to Scotland in an economical and efficient way, while supporting jobs, in particular giving great opportunities to young people through apprenticeships and graduate programmes".
He said Caledonia Alliance had committed to employing 20 modern apprentices and seven graduates, and BBV Alliance would hire 30 modern apprentices and 18 graduates.
Scottish Water said "an element" of the alliances' programme would be self-delivered and the remainder delivered through contract partners. It said the alliances were now working with Scottish Water to procure 'Tier One' suppliers.
The utility is also seeking contract partners for its infrastructure and capital maintenance budget over the six years.
It will stage 'market days' in Sumburgh, Kirkwall and Inverness next week, followed by similar events in Stornoway, Pitlochry, Dumfries & Galloway and the Borders over the next month.
Mr Aitkenhead said: "These rural framework market days will help identify contract partners who can be part of a capital maintenance programme estimated to be around £500 million over the six years.
Douglas Millican, chief executive of Scottish Water, said: "Our delivery programme is geared to get the best teams to help us deliver our investment programme. We will also provide benefit to communities across Scotland through businesses that can work in our rural framework and help deliver the investment their community needs."