Add potatoes to slow cooker.
Pour water and chicken broth over potatoes. Cover and cook on high 3-4 hours or on low, 5-6 hours, or until potatoes are tender.
When potatoes are ready, drain liquid. Add in butter, Greek yogurt, garlic, salt, pepper, and cheese.
Using a potato masher or electric hand mixer, mix until potatoes have reached your desired consistency. If needed, milk and/or more Greek yogurt can be added.