Thanks all. I'll give your suggestions a try. The water is OK out of the tap. I might do a test with the hose disconnected. It is frustrating and weird because so many say their Camelbak is fine.

Maybe my water reacts with the materials? I have cleaned and dried the life out of the thing in various ways but will try again. I wouldn't think this necessary though.

Platypus might be worth a shot.

Cheers