In a medium saucepan combine the water, peppers and onion, boil until tender.
Pour the mixture into a food processor and puree.
In a large stock pot heat the chicken stock over high heat.
Add the vegetable puree, butter, half-and-half, salt and pepper.
Reduce the heat to simmer.
Dissolve the cornstarch in a small amount of cold water.
Stir in the cornstarch, and cook the soup until thickened.