OH dear. Just how bad off are your kidneys? When were your last lab tests, and what did you get for Creatinine and BUN?
If you're not retaining water or swelling at all, then you can take in a bit of salt. Salt will help you regulate your water balance. It's best to get organic salt, such as in Bieler Broth, because getting it from veggies means you get potassium too so that the two don't get out of balance.