When your dog is both drinking a lot of water and acting lethargic, it’s often more than just a tired day. These symptoms combined can be early signs of serious underlying health conditions affecting major organs, hormones, or the immune system.
We outline the common causes of dog drinking a lot of water and lethargic, what you can do at home, and when to seek veterinary help.
Dog Drinking a Lot of Water and Lethargic — Why It Happens
Excessive water intake and low energy levels may signal infections, endocrine disorders like diabetes or Cushing’s disease, kidney failure, liver disease, or toxin exposure. These conditions disrupt the body’s balance and often leave dogs feeling weak, uncomfortable, or unwell.
Common Causes of Dog Drinking a Lot of Water and Lethargic
Kidney Disease
When a dog’s kidneys are compromised, they lose the ability to filter waste properly and conserve water.
This leads to excessive urination, dehydration, and increased thirst. As toxins build up in the bloodstream, dogs often feel nauseous, lose their appetite, and become lethargic.
You may also notice pale gums, bad breath (ammonia-like odor), vomiting, or weight loss.
Chronic kidney disease is diagnosed through bloodwork (elevated BUN/creatinine), urinalysis, and sometimes ultrasound. It’s not curable, but can be managed with diet, hydration support, and medications.
Diabetes Mellitus
In diabetic dogs, glucose builds up in the blood and pulls fluid into the urine, causing excessive thirst and urination.
Without insulin to help move glucose into cells, dogs lose energy and become sluggish. Weight loss, increased appetite, urinary accidents, and sweet-smelling breath are other signs.
Diagnosis is confirmed with blood and urine tests. Treatment involves insulin therapy, dietary control, and regular monitoring.
Cushing’s Disease
Cushing’s causes the adrenal glands to produce too much cortisol. Dogs with Cushing’s often drink and pee more, pant excessively, and appear tired or less interested in activities.
You might notice a pot-bellied appearance, hair thinning, or fragile skin.
Because symptoms are subtle and build over time, Cushing’s can be hard to spot early. Diagnosis involves hormone tests and imaging.
Infections (Bacterial or Viral)
Serious infections like leptospirosis, pyelonephritis, or parvovirus can cause increased drinking as the body tries to stay hydrated.
Lethargy, vomiting, fever, and diarrhea often follow as the immune system struggles to fight the infection.
These illnesses require immediate veterinary attention, especially in puppies or unvaccinated dogs.
Read more: Dog Drinking a Lot of Water and Panting (What It Means)
Liver Disease
The liver plays a key role in detoxifying the body, processing nutrients, and producing energy. When it’s inflamed or failing, dogs may drink more, lose appetite, and seem weak.
Look for yellowing of the eyes or gums (jaundice), vomiting, or behavioral changes like confusion or pacing.
Blood tests and imaging can help detect liver disease early. Treatment depends on the cause but may include diet changes, antibiotics, or supportive medications.
Toxin Exposure
Ingesting certain household items—like antifreeze, human medications, or poisonous plants—can cause immediate thirst and rapid decline in energy.
Symptoms may also include vomiting, seizures, pale gums, or disorientation.
If you suspect your dog has ingested a toxin, treat it as a medical emergency. Quick veterinary care can be life-saving.
What to Do If Your Dog Is Drinking a Lot and Acting Lethargic
Provide clean water at all times but monitor how much your dog is drinking and urinating.
Avoid any sudden dietary changes, treats, or human foods that might stress your dog’s system.
Encourage rest and keep them in a cool, quiet place while monitoring their energy, appetite, and bathroom habits.
Note any additional symptoms such as vomiting, diarrhea, changes in breathing, or skin abnormalities.
Call your vet promptly. Provide a detailed history including the timing of symptoms, diet, environment, and any medications or supplements your dog is taking.
When to Call or Visit Your Vet
Get veterinary help right away if your dog:
Is very weak, slow to get up, or refusing to move
Is drinking far more than usual for more than a day
Has vomiting, diarrhea, or loss of appetite
Has yellow eyes, gums, or skin
Shows signs of disorientation, panting, or collapse
Veterinarians will typically perform bloodwork, urinalysis, and sometimes imaging (ultrasound, X-ray) to pinpoint the cause.
Read more: Dog Drinking a Lot of Water and Losing Weight (Here’s Why)
Key Takeaway
A dog that’s drinking a lot and acting lethargic may be fighting off a serious condition—from kidney or liver disease to diabetes or infection.
Don’t wait to see if it passes. Early intervention and diagnostic testing can help get your dog the treatment they need—and prevent symptoms from spiraling into an emergency.