Water 4 month old

Brandi

My son is four months old and is a little overweight my doctor told me to give him water instead of formula or breast milk on occasion but every time I do I feel very guilty I feel like if he cries cause he's hungry he should have milk what is y'all's opinion? She also said apple juices OK so I got the baby kind and put half an ounce of apple juice in 3 ounces of water and I still feel terrible about it. Thanks everyone!