In your slow cooker, combine chicken broth, water, package of Rice-a-Roni (including seasoning packet), carrots, celery, and basil. Stir to combine.
Add in uncooked chicken breasts.
Cook on low for 7-8 hours, or high for 4.5 hours.
In a small saucepan, melt butter over medium heat. When melted, whisk in flour. Slowly, very slowly pour in half and half until well combined. Stir in salt and black pepper.
Remove chicken breasts from the slow cooker and chop them into chunks.
Pour the creamy mixture into the slow cooker and stir to combine. Add chicken chunks back in and cook for 15 minutes longer.
Makes about 10 cups of soup. Serve with crusty bread and enjoy!