Bring water, broth, and salt to boil in a small saucepan.
While that is coming to a boil, peel and slice the potatoes into 1/4-inch rounds. If water comes to a boil before you are done, just turn the heat down. You don't want to expose the potatoes to air for long once they are peeled because they will turn brown.
Place potato slices in the crockpot and pour boiling water mixture on top. Stir to coat potatoes.
Brush the potatoes on top with melted butter. Press a piece of parchment paper that is slightly larger than the crockpot on top of the potatoes and tuck edges down to hold in place.
Cover and cook on HIGH until all the potatoes are tender, about 4 hours.
Discard parchment paper. Sprinkle the butter pieces on top of the potatoes. Use a potato masher to mash potatoes until smooth.
Mix in the sour cream, chives, garlic powder, and pepper. Taste for seasoning and add extra salt if desired.