Rinse the roast and pat dry with paper towels.
Layer onions in the bottom of a large slow cooker.
Place the roast in slow cooker; sprinkle half the spices over the roast and lightly rub them into the meat.
Turn the roast over and season with the remaining spices.
Pour the water and wine into the slow cooker.
Add potatoes around the roast.
Cover and cook on low for 9-10 hours or on high for 6-7 hours, until the meat is falling apart.
When the meat is done cooking, shred gently with two forks and then toss in the juices to keep it moist until ready to serve.