Understanding Water Balance and Hydration in Dogs

“ It is our job to anticipate the dog’s needs and to make the water attractive enough so he will drink in preparation for physical or stressful activities…prevention of dehydration is the preferred method.”

-Dr Arliegh J Reynolds, Veterinary Surgeon, PhD
Associate Professor of Clinical Nutrition, College of Veterinary Medicine, Cornell University, New York.

Water is the most essential, yet often the most overlooked, of all nutrients. Owners spend a lot of time figuring out what and how much food they should feed their dogs. However, we must remember that training, showing and exercising changes a dog's water requirements at least as dramatically as its requirements for energy, protein, vitamins and minerals.

A dog may tolerate a dietary deficiency in one of these nutrients for several days or even weeks before any adverse effects on its performance or health are observed. In contrast, dehydration may lead to immediate diminished performance and, in severe cases, even to death within hours of its onset.  

The factors which contribute to water loss in a dog are complex and constantly changing. Dr Reynolds and other Veterinary Research shows: Beware the panting dog!

Exercise is a key factor that causes the most remarkable increase in water loss observed in active dogs. This is due to the increase in evaporation from the mouth and respiratory tract. Depending on the dog's exercise intensity, and the environmental temperature and humidity, evaporative water losses may increase 10-20 fold during exercise, or 85 to 150 grams per hour [1][2] [3]Dog owners may not recognize how much water their dog is losing because dogs pant to cool rather than sweat through their skin, hence this water loss is not obvious.

Dog can lose 6% of body weight before stimulated to drink. The health concern is that there is a time delay from the need to drink water and when the dog experiences the dehydration necessary to stimulate drinking.[4] O’Connor’s research found that a dog can lose up to 6% of body weight before stimulated to drink.[5] Dogs, like humans, need to drink BEFORE & DURING exercise. Prevention is better than cure. During this time delay the dog will experience significantly higher body temperature, reduced cardio output, and blood flow.[6][7][8][9] These negative health effects are the same for humans. This is the reason humans now know to drink before feeling thirsty and ‘drink 8 cups of water a day’, to prevent even mild dehydration.

Human Health Professionals tell us, if you wait to drink when you are thirsty, you cannot drink enough during exercise to rehydrate. Successful athletes drink prior to and in the early stages of the race, before they become thirsty.

Research shows dogs should drink before exercise. Recommended amount is 500 ml [10]or 10ml/kg body weight[11] 20-30 minutes prior to the exercise. For endurance activities, dogs should take more frequent water breaks.

Dr Reynold’s concluded specifically in his research “Flavouring the water to make it more palatable has long been a successful way of getting dogs to drink.” Prevention is much better than cure when it comes to water loss.

Dog Owners can test effects of hydration for themselves very simply:

Quantity of water lost: 1) Place hand in front of heavily panting dog, 2) feel the water content and/or weigh dog before & after moderate to heavy exercise.


[1] A Reynold. Hydration Strategies for Exercising Dogs, In Reinhart, GA and Carey DP, eds, Recent Advances in Canine and Feline Nutrition Volumn 11. Wilmington, OH, Orange Frazier Press, 1998 259-267

[ 2] WJ O’Connor, Drinking by Dogs during and after running, American Journal of Physiology, 1975 Sep;250(2): 247-59

[3] Dr Pigott, Veterinary Surgeon, Study, Jack Russel 7kg lost 350gr in 40min, Rockwieller 28.2 kg lost 900gr over 10km (no urination), Sydney, Australia, Feb 2005

[4] DJ Ramsey, Rolls BJ, Wood RJ, Thirst following water deprivation in dogs, American Journal of Physiology, 1977 Mar;232;(3):R88-92

[5] WJ O’Connor, Drinking caused by exposing dog to radiant Heat, American Journal of Physiology, 1977 Jan;264 (1):229-37

[6] MA Baker, Thermoregulatory responses to exercise in dehydrated dog, American Journal of Applied Physiology, 1984 Mar:54(3):635-40.

[7] MA Baker, Cardivasular and respiratory response to heat in dehydrated dog, American Journal of Applied Physiology, 1984 Mar:426(3 Pt 2):R369-74

[8] MA Baker, E Turlejska, Thermal panting in dehydrated dogs: effect of plasma volume expansion and drinking, American Division of Biomedical Sciences, University of California, 1989 Mar:413(5):511-5

[9] LW Chapman, Baker MA, Cardiac output of dogs exercising in the heat, American Journal of Physiology. 1984 Jul (1 Pt 2):R124-6.

[10] A Reynolds, 1998, recommendation based on 20kg Dog for short intense sprint activities.

[11] O’Connor, 1975 et al,"