In a medium pot, bring the water and stock to a boil over high heat.
Add the lemongrass, galangal, kaffir lime leaves, fish sauce and tamarind paste. Break apart the tamarind paste with a wooden spoon in the hot liquid until it is dissolved.
Add the onion, chili paste and mushrooms and boil for about 7 minute more.
Add the chili peppers, tomatoes, shrimp and chicken and cook until the proteins are firm and the shrimp have turned orange, about 7 minutes.
Turn off the heat and add the lime juice and fresh cilantro leaves. Add additional fish sauce to taste and serve with lime wedges on the side.