Whisk all ingredients together in a saucepan, adding the water last. Start with a cup of water, then whisk in a bit more at a time, until it reaches a consistency than barbecue sauce. I ended up using about 1 ½ cups of water, but it will vary depending on how thick your tomato paste is.
Bring to a gentle boil at medium-high heat, then reduce to medium-low. Simmer, stirring frequently, for 20 minutes, or until slightly thickened.
Taste and adjust sweetener or cayenne pepper if you prefer the sauce to be sweeter or spicier. If it's still thicker than you like, you can stir in additional water, a tablespoon at a time, until reaching desired consistency.
