Polydipsia can be defined as a horse that drinks more than 12 gals per 1000 lbs. (100 ml / kg) of body weight (BW) a day. Polyuria would be greater than 6 gals of urine (50 ml / kg) per 1000 lb. of BW / day. Both these figures are above average but represent the high end of the normal range. Some normal horses may have higher consumption and output and some horses with disease may be lower but this is a good starting point.

There are many causes for excessive drinking and urination and they can occur at both ends of the horse for entirely different reasons. The horse may be drinking an excessive amount of water and therefore need to urinate a lot or the horse many not be able to concentrate his urine leading to excessive water loss and therefore be thirsty continuously. This article discusses the various causes, diagnosis, treatments, and prognosis.