By Caroline Buck, Co-founder of Petaluma
Most of us notice when the water bowl runs dry, but few of us know how much our dogs should drink in a day. Water supports digestion, circulation, and temperature control, and needs shift with heat, exercise, diet, and age. Older dogs bring their own changes, and a sudden jump in drinking can be an early sign of illness. So how much water does your dog need? Below, we cover daily water needs, signs of dehydration, hot-weather risks, and hydration tips for senior dogs.
Quick Answer
Most healthy adult dogs need roughly 2/3 to 1 ounce of water per pound of body weight each day, including the water in their food. That works out to about 3.5 to 5 cups a day for a 40 lb dog (Merck Veterinary Manual). Dogs need more in hot weather and after exercise. For senior dogs, watch for changes in drinking habits, since a sudden increase can be an early sign of kidney disease, diabetes, or Cushing's disease.
In This Article
How much water does a dog need?
About 2/3 to 1 ounce per pound of body weight per day. The Merck Veterinary Manual puts the water needs of most mammals at rest at about 44 to 66 mL per kilogram of body weight each day (Merck Veterinary Manual). That total includes the water in your dog's food, not just what they drink from the bowl.
| Dog's weight | Approximate water per day |
|---|---|
| 10 lb | About 0.75 to 1.25 cups |
| 20 lb | About 1.75 to 2.5 cups |
| 40 lb | About 3.5 to 5 cups |
| 60 lb | About 5 to 7.5 cups |
| 80 lb | About 7 to 10 cups |
Calculated from 44 to 66 mL per kilogram per day (Merck Veterinary Manual). Amounts include water from food. Needs rise with heat, exercise, and dry food.
Healthy dogs with steady access to clean water are good at drinking what they need. Merck notes that healthy animals can "effectively self-regulate their intake" and that water should not be restricted. Most pet parents do not need to measure water. The more useful habit is noticing when your dog drinks noticeably more or less than usual.
Why hydration matters
Water carries nutrients into cells, removes waste through the kidneys, and helps dogs digest food. It also helps dogs cool down, since panting releases heat through evaporation. Dogs lose water through urine, stool, and breathing, so they need to replace it every day.
Signs of dehydration in dogs
Mild dehydration is hard to spot at home. Veterinarians look for these signs as dehydration becomes more noticeable (Merck Veterinary Manual):
- Dry or tacky gums: Healthy gums feel slick and moist to the touch.
- Skin tenting: When you gently lift the skin between the shoulder blades, it should snap back quickly. Skin that returns slowly can signal dehydration.
- Sunken eyes: Eyes that look sunken suggest more advanced dehydration.
- Sudden weight loss: Rapid weight loss over a day or two often reflects lost water.
The skin test is less reliable in older and very thin dogs. Their skin can tent and their eyes can look sunken even when they are well hydrated (Merck Veterinary Manual). If your dog is vomiting, has diarrhea, or will not drink, call your veterinarian.
Hydration and the senior dog
Watch for changes in drinking habits
A change in how much your older dog drinks is worth raising with your veterinarian. The 2023 AAHA Senior Care Guidelines list an altered thirst pattern among the signs of illness in senior dogs (AAHA, 2023). Increased thirst can be an early sign of several conditions that become more common with age:
- Kidney disease: Excessive thirst and urination are usually the earliest signs (Merck Veterinary Manual). Our guide to managing chronic kidney disease in dogs covers the stages and diet.
- Diabetes: Diabetes mellitus is one of the most common causes of increased thirst and urination (Merck Veterinary Manual). Read more in our post on diabetes in dogs.
- Cushing's disease: Cushing's occurs mostly in dogs aged 7 to 12, and increased thirst is one of its most common signs (Merck Veterinary Manual). Our Cushing's disease guide explains the signs and diet.
Other causes include liver disease and some infections. A vet can usually narrow it down with bloodwork and a urine test.
Make water easy to reach
Older dogs with stiff joints may walk to the water bowl less often. These changes make drinking easier:
- More bowls: Put water in more than one room. Merck notes that multiple water sources encourage dogs to drink (Merck Veterinary Manual).
- Raised bowls: AAHA includes raising food and water bowls among comfort measures for senior dogs with pain (AAHA, 2023).
- Good footing: Place bowls on a rug or mat so your dog does not slip on hard floors.
Take extra care in the heat
Older dogs are more vulnerable to heat. In a UK study, dogs aged 12 and older had about nine times the odds of fatal heat-related illness compared with young dogs. The researchers linked this to older dogs' reduced ability to regulate body temperature (Hall et al., 2022).
Adding water to your dog's food
Adding water to your dog's food is a simple way to add water to their day. Dry foods contain about 3% to 11% water, while canned foods contain about 60% to more than 87% (Merck Veterinary Manual). Dogs on dry food make up the difference by drinking more, so both approaches can keep a healthy dog well hydrated.
Petaluma's baked food softens well in water. Customers tell us that moistening it helps older dogs and dogs who find hard food difficult to chew. You can see how it softens in our soaking video. If you flavor water or food with broth, choose one made without onion or garlic, including onion and garlic powders. Both are toxic to dogs (Merck Veterinary Manual).
Keeping dogs hydrated in hot weather
Exercise causes most heatstroke in dogs. In a UK study of heat-related illness, 74% of cases followed exercise, and most of those happened after a walk (Hall et al., 2020). Some dogs face higher risk:
- Flat-faced breeds: Brachycephalic dogs such as Bulldogs and French Bulldogs had about twice the odds of heat-related illness (Hall et al., 2020).
- Large and overweight dogs: Dogs over 50 kg (110 lb) and dogs above their breed's average weight had higher odds.
- Certain breeds: Chow Chows, Greyhounds, and Golden Retrievers had higher odds than Labrador Retrievers.
- Senior dogs: Dogs 12 and older had higher odds, as covered above.
On hot days, walk in the cooler morning or evening, carry water on outings, and offer frequent chances to drink (Cornell Riney Canine Health Center). Give your dog shade and a cool place to rest at home. Heatstroke is an emergency, so call your veterinarian right away if your dog seems overheated.
For more on caring for an aging dog, see our guide to how much to feed a senior dog and our Q&A with Dr. Blake Hawley, DVM on our senior formula.
Baked Food That Softens in Water
Petaluma's plant-based baked food is formulated by veterinary nutritionists and softens easily when moistened, which many older dogs appreciate. Try a free sample for the cost of shipping.
Frequently asked questions
How much water should a dog drink a day?
Roughly 2/3 to 1 ounce per pound of body weight per day, including the water in food. That is about 3.5 to 5 cups for a 40 lb dog, based on the Merck Veterinary Manual. Dogs need more in hot weather, after exercise, and on dry food.
How can I tell if my dog is dehydrated?
Check for dry or tacky gums, skin that is slow to snap back when gently lifted, sunken eyes, and sudden weight loss, according to the Merck Veterinary Manual. Mild dehydration is hard to see, and the skin test is less reliable in older dogs. Call your vet if your dog is vomiting, has diarrhea, or will not drink.
Why is my older dog drinking so much water?
Increased thirst in an older dog can be an early sign of kidney disease, diabetes, or Cushing's disease, according to the Merck Veterinary Manual. Heat, exercise, and a change to drier food can also raise thirst. If the increase is new and lasts more than a few days, ask your vet about bloodwork and a urine test.
Is it OK to add water to my dog's food?
Yes. Adding water to food adds to your dog's daily water intake, and dogs eating moist food tend to drink less from the bowl, according to the Merck Veterinary Manual. Moistening food can also make it easier for some older dogs to eat.
Which dogs are most at risk in hot weather?
Flat-faced breeds, large and overweight dogs, and senior dogs face the highest risk. In UK studies, brachycephalic dogs had about twice the odds of heat-related illness, and most cases followed exercise (Hall et al., 2020).
References
- Merck Veterinary Manual. Nutritional Requirements of Small Animals. merckvetmanual.com
- Merck Veterinary Manual. The Fluid Resuscitation Plan in Animals. merckvetmanual.com
- Merck Veterinary Manual. Noninfectious Diseases of the Urinary System in Dogs. merckvetmanual.com
- Merck Veterinary Manual. Diabetes Insipidus in Animals. merckvetmanual.com
- Merck Veterinary Manual. Cushing Disease (Pituitary-Dependent Hyperadrenocorticism) in Animals. merckvetmanual.com
- Merck Veterinary Manual. Garlic and Onion (Allium spp) Toxicosis in Animals. merckvetmanual.com
- Dhaliwal R, Boynton E, Carrera-Justiz S, et al. 2023 AAHA Senior Care Guidelines for Dogs and Cats. Journal of the American Animal Hospital Association. 2023;59(1):1-21. doi:10.5326/JAAHA-MS-7343. doi.org/10.5326/JAAHA-MS-7343
- Hall EJ, Carter AJ, O'Neill DG. Incidence and risk factors for heat-related illness (heatstroke) in UK dogs under primary veterinary care in 2016. Scientific Reports. 2020;10:9128. doi.org/10.1038/s41598-020-66015-8
- Hall EJ, Carter AJ, O'Neill DG. Dogs don't die just in hot cars: exertional heat-related illness (heatstroke) is a greater threat to UK dogs. Animals. 2020;10(8):1324. doi.org/10.3390/ani10081324
- Hall EJ, Carter AJ, Chico G, et al. Risk factors for severe and fatal heat-related illness in UK dogs: a VetCompass study. Veterinary Sciences. 2022;9(5):231. doi.org/10.3390/vetsci9050231
- Cornell University Riney Canine Health Center. Heatstroke: A medical emergency. vet.cornell.edu
This article is for educational purposes and does not replace advice from your veterinarian.
About the author
Caroline Buck is the co-founder of Petaluma, a plant-based dog food company she started after struggling to find nutrition that was both healthy for her dogs and gentler on the planet. Petaluma's recipes are formulated by veterinary nutritionists, and Caroline writes about canine nutrition, senior dog health, and sustainable feeding for pet parents. Learn more about Petaluma.
