Excessive liquid consumption

Hi, My brother (David)has a chemical imbalance and is also schizophrenic.He has been this way since the age of 15. Dr.s say it is due to a tramatic experience,They concluded the cause being our fathers death (My brother and his dad were very close) He is now 46 years old and lives with our mom who is 75. He has a OCD about consuming liquids.His thirst seems to be unquenchable. We have spoken to his DR's about this being a side effect of his meds they said it could be a slight contributor but not the main cause. He has been on several different meds and this OCD has remained steady through them all. WE have asked his DR to prescribe something to help control the urge to consume so much liquids but they don't.He landed himself in the hospital for washing away most of the sodium/potassium leaving him with dangerously low levels actually causing him to have a seisure. Is there anything homeopathic that will at least decrease the urge to dring so much. we are in fear that he will once againg lower his sodium and this time he won't be so lucky.