In a large pot, combine chicken pieces and water.
Bring to a boil over medium-high heat.
Skim off any foam that rises to the top.
Add the onion, garlic, and cumin to the pot.
Reduce heat to low and simmer for 30 minutes.
Add carrots, celery, and potatoes to the soup.
Season with salt and pepper to taste.
Simmer for another 20 minutes until vegetables are tender.
Stir in the chopped tomato and cook for 5 more minutes.
Garnish with fresh cilantro before serving.