In 3 1/2- to 6-quart slow cooker, place chicken thighs and onion. In small bowl, mix broth and paprika. Pour over chicken. Sprinkle with salt.
Cover; cook on Low heat setting 7 to 8 hours.
About 15 minutes before serving, with slotted spoon, remove chicken and onion from slow cooker; place on serving platter. Cover to keep warm.
In small bowl, blend water and cornstarch until smooth. Stir into liquid in slow cooker. Increase heat setting to High. Cover; cook 8 to 10 minutes longer or until thickened. Stir in sour cream. Pour sauce over chicken.