Since you are all so sweet and concerned about Mr. K, I shall keep you posted. The three possibilities are: Diabetes Insipidus, lymphoma, and kidney tumours. Next step, ultrasound with specialist to determine whether it's one of the latter two rather disastrous possibilities, with biopsy being done on the spot if there are tumours found.
Oh, damn. Damn, damn, damn.
Well, we shall see. More to be found out, still.