Bring water to a boil in a large saucepan.
Add potatoes, garlic and 2 teaspoons salt and cook at a brisk simmer until potatoes are tender, about 15 minutes.
Drain potatoes and garlic, reserving 1 cup of cooking liquid. Mash potatoes and garlic.
Beat in olive oil and then thin to desired consistency with reserved cooking liquid. Check seasoning and serve.