I don't know how long this has been going on, but I'll tell you about our first greyhound Jimmy. When the cold weather came and we first turned the heat on for the season, he would drink huge amounts of water and consequently have accidents. This happened every year for the last few years we had him. The air was too dry I suppose. As the cold weather continued he would acclimate, but every year in the fall this would happen several times before he adjusted. Just a thought......I think it's good you've had the other tests run. Hope you are able to get to the bottom of it soon.