Add water, garlic cloves, peeled and cubed potatoes, water, pats of butter, chopped rosemary and 1 teaspoon kosher salt to bottom of a 5 quart or larger slow cooker.
Cover and cook on LOW for 6 to 8 hours or on HIGH for 3 to 4 hours until potatoes are tender when pierced with a fork.
Turn off slow cooker and set lid aside and let potatoes cool in slow cooker for 5 minutes.
Mash potatoes with a potato masher right in the slow cooker until the potatoes are mostly mashed.
Add half and half and cream cheese and continue to mash until the desired consistency is reached. Taste and add additional salt and pepper as needed.
Transfer mashed potatoes to a serving bowl or serve straight from the slow cooker by turning the temperature down to WARM for up to 3 hours. Garnishing the top of the potatoes with fresh rosemary sprigs if desired.