Could also be the beginnings of diabetes. I've had 3 dogs with diabetes. Both drank tons of water and had dilute urine until the lab work finally showed diabetes. One dog had many strange symptoms that never ever pointed to diabetes, the other had high glucose within 1 month of the increase fluid intake and urination changes. Both were treated with insulin. One had to be put down due to complications(after 4mos. of treating) at at 8yrs, the other (with the worse symptoms including blindness) is still going strong and will be 13yrs soon. The third dog is now 10 and doing well.