Why Is My Cat Drinking a Lot of Water and Losing Weight?

You might wonder what counts as “a lot” of water or “too much” weight loss. Here’s how to tell if it’s an issue for your cat.   

The average cat typically needs about 4 ounces of water per 5 pounds of body weight each day. For example, a 10-pound cat should drink about a cup of water daily (this can include moisture from food). 

But that’s not always easy to measure in real life, so it’s best to monitor their habits and ask:  

• Are you refilling their water bowl more often?  
• Are they visiting their water bowl more frequently?  
• Are they seeking out unusual water sources, such as the sink or toilet?  
• Are they going to the litter box to urinate more often?  
• Are they having accidents? 

If the answer is yes, those changes can be clues that something’s off. 

If your cat is losing weight unintentionally, especially more than 1–2% of their body weight each month, something could be wrong. 

Compare your cat’s previous weight with their current weight. You can also evaluate their past and current body condition score (BCS), which takes into account their frame, muscle tone, and overall build.  

If your cat’s ribs look or feel more pronounced or their waist appears slimmer than usual, it could signal a problem. 

If you notice your cat drinking a lot of water and dropping pounds, several underlying health conditions could be to blame. The most common include:  

• Diabetes mellitus: Without enough insulin to regulate blood sugar levels, your cat’s system may break down fat and muscle for fuel, resulting in an increased appetite and weight loss. Elevated blood sugar levels contribute to drinking more water and frequent peeing. 
• Chronic kidney disease: The most common reason senior cats start peeing and drinking more than usual is chronic kidney disease (CKD), although it can occur in any age cat. CKD impairs the kidneys’ ability to concentrate urine, leading to excessive thirst and a reduced appetite.  
• Hyperthyroidism: The overproduction of thyroid hormones speeds up metabolism, often resulting in weight loss and excessive drinking.  
• Liver disease: When the liver isn’t functioning properly, it can cause increased thirst and urination, loss of appetite, yellowing of the skin or mucous membranes, and weight loss. 
• Steroids: Increased thirst and appetite are side effects of corticosteroids (such as prednisone or prednisolone). 
• Cancer: Some cancers in cats, such as lymphoma, kidney cancer, or liver cancer, can lead to unexplained weight loss and changes in drinking habits. 

If your cat is suddenly drinking more water and dropping pounds, don’t wait it out—schedule a vet visit.  

Your vet will start by giving your cat a full nose-to-tail exam and asking questions about their habits and any recent changes.  

From there, they’ll likely run some tests, including: 

• Blood work: To check kidney and liver function, thyroid hormone levels, and blood sugar. 
• Urinalysis: To see how well the kidneys are working and look for glucose, protein, or bacteria. 
• X-rays or ultrasound: For a closer look at the organs. 

Once your vet has diagnosed your cat, they’ll prescribe a treatment, which depends on their condition: 

• Diabetes: Daily insulin injections, diabetic support cat food, and regular blood sugar monitoring.  
• Kidney disease: Hydration support, a prescription kidney cat food like Royal Canin Veterinary Diet Adult Renal Support, and medications to control nausea, blood pressure, or anemia.  

• Hyperthyroidism: Oral or topical medication (methimazole) to regulate thyroid hormone levels and possibly radioactive iodine therapy, surgery to remove the thyroid gland, or a prescription low-iodine cat food, such as Hill’s Prescription Diet y/d Thyroid Care Dry Cat Food.  

• Liver disease: Special diets, supplements such as SAMe or milk thistle, and oral medications. 

• Cancer: Surgery, radiation therapy, chemotherapy, or palliative care. 

Never offer your cat treatment without the approval of your veterinarian.  

After the vet visit, there are steps you can take to help your cat feel more comfortable at home.  

Place extra water bowls throughout your home or try a cat fountain, such as the PawsPik SS-01 Stainless Steel Cat Fountain. 

Your cat is likely making extra trips to the litter box, so keep it accessible and clean: 

• Add an extra box if you have multiple cats: Follow the golden rule—one litter box per cat, plus one extra to prevent crowding, increase cleanliness, and reduce accidents.  
• Choose the right box: A larger box, like the Petmate Litter Pan (Jumbo size), gives your cat more space to do their business. If your cat has mobility issues or arthritis, try a low-entry option, such as the Frisco Senior & Kitten Cat Litter Box. 

• Use unscented litter: Strong fragrances can turn cats off. Try an unscented, clumping litter, such as Tidy Cats Free & Clean Unscented Clumping Clay Cat Litter.  

Cats with chronic illness often tire easily, so provide soft beds, such as the Bedsure Round Orthopedic Bolster Bed or the Frisco Sherpa Bolster Cat Bed. 

In addition to following your vet’s instructions, you can also keep a weekly log of how much your cat is eating and drinking, as well as their weight. This information can help your vet adjust your cat’s treatment plan, if needed, at your next visit. 

Should I be concerned if my cat is drinking a lot of water? 

While cats may drink more on hot days or when only eating dry food, an increase in thirst may signal a health issue. If you’re refilling the water bowl more than usual, schedule a vet visit. 

Do cats drink more water if they’re sick? 

Yes. Many medical conditions cause excessive thirst (polydipsia) as the body’s way of trying to flush out toxins or balance fluids. Illnesses that affect the kidneys, thyroid, or blood sugar are the most common culprits.  

Is my cat too skinny if I can feel their spine? 

Yes, probably. If you can easily feel or see your cat’s spine, they’re likely underweight. Noticeable or sudden weight loss always warrants a visit to the vet.  

Is a cat losing weight always a red flag? 

No, not if it’s intentional. If your cat is on a vet-approved diet or exercise plan, gradual weight loss is expected and healthy. However, if the weight loss is unintentional or happens quickly, it’s a red flag and should be checked out by a vet as soon as possible.