Hi, I'm not familiar with the Keto diet exactly, but I have heard that you should aim to drink half of your body weight in ounces per day. Especially if you are on a high protein diet. Your kidneys need water to flush and process all of the protein. That is my understanding. Not sure why you would be retaining water like that, except maybe if you are having a lot of sodium in your diet. I take in a lot of sodium per day, but with drinking 100 oz. of water a day I think I typically flush it out. Hope this helps. If it continues, I would recommend going to the doctor to get it checked out. Good luck!