In a soup pot, mix water and canned soup until smooth. Stir in diced onion and potato.
Bring to a boil, then reduce heat and simmer for 10 minutes stirring occasionally.
Add thawed vegetables, bring back to a boil. Reduce heat and simmer for another 8 to 10 minutes until potatoes are tender, stirring occasionally. Remove from heat and stir in cubed Velveeta until melted. Serves 4-5.