We Have A 6 Year Old Great Dane With Lumps

We have a 6 year old great dane with lumps we thought may be 'just cysts' . vet opinion is that it may be lymphoma...we are awaiting cytology. he is not quite himself......keen to look for food and will eat quite readily- but flatly refuses to drink any water....he is on diuretics because of fluid around heart .... we have given him food with extra fluid in it to help out...but he is not keen on water at all!!