Combine chicken broth, water, carrots, celery, the package of dry rice and seasoning packet (included in box) into a slow cooker. Stir together and put chicken breasts inside.
Cover with lid and cook on low for 6-8 hours.
Slowly add in the half-n-half milk while whisking until smooth and incorporated. Cook and stir for a few minutes until slightly thickened. This won't take long.
Pour into the slow cooker, stir together to combine, and let cook on low for an additional 30 minutes. Serve!
If your chicken breasts are small then use 3 of them. It should be at least 1 lb of chicken. Slightly more won't hurt.
You can use full fat half & half milk or fat free
DO NOT prepare the rice mix before adding it into the slow cooker. Be sure and not throw out the seasoning packet included in the rice box. You will add that into the slow cooker with the other ingredients.
Watch carefully what rice box you buy at the store. It should be the regular rice-a-roni NOT the instant or quick stuff. This is the wild rice you want.