Heat the oil in a soup pot over medium heat. Add the onion and garlic and cook, stirring, until soft, about 6 minutes.
Add the squash, water, and cider and season with salt and pepper. Bring the soup to a boil, lower the heat, and simmer, until the squash is tender, about 30 minutes.
Using an immersion blender, puree the soup until smooth. Divide the soup among bowls and garnish with the croutons. Serve immediately.
