When an older cat starts drinking noticeably more water, it almost always signals an underlying health issue. Increased thirst is one of the most common reasons senior cats visit the vet, and the three leading causes are chronic kidney disease, hyperthyroidism, and diabetes. A healthy 10-pound cat typically drinks about one cup of water per day (roughly 4 ounces per 5 pounds of body weight). If your cat is consistently exceeding that, or you’re refilling the bowl more often than you used to, something is likely driving that change.
How to Tell if Your Cat Is Actually Drinking More
Cats are subtle creatures, so it’s worth confirming what you’re seeing before jumping to conclusions. The simplest method is to measure the water you put in the bowl each morning using a measuring cup, then measure what’s left at the end of the day. Do this for three or four days to get a reliable average. If you have multiple pets sharing a water source, you’ll need to isolate your cat’s bowl temporarily to get an accurate read.
Keep in mind that cats on wet food get a significant portion of their water from the food itself, so a cat eating only dry kibble will naturally drink more from a bowl. A recent switch from wet to dry food can explain a bump in water intake without anything being wrong. But if the diet hasn’t changed and your cat is consistently drinking well above one cup per day (for an average-sized cat), that’s worth investigating.
Chronic Kidney Disease
This is the single most common reason older cats drink more water. By some estimates, the majority of cats over 15 show at least some degree of kidney decline. As the kidneys lose their ability to concentrate urine effectively, your cat produces larger volumes of dilute urine and then drinks more to compensate. You’ll often notice the litter box is wetter or heavier than usual before you notice the increased drinking.
Kidney disease in cats tends to develop gradually over months or years. In the early stages, blood work can look completely normal because the kidneys have significant reserve capacity. A newer blood marker called SDMA can detect kidney problems earlier than traditional tests, sometimes catching disease before your cat shows any symptoms at all. The condition can’t be reversed, but when caught early it can often be managed with diet changes and supportive care that slow progression and keep cats comfortable for years.
Hyperthyroidism
An overactive thyroid gland is extremely common in cats over 10 and produces a recognizable cluster of symptoms: weight loss despite a ravenous appetite, increased thirst and urination, restlessness, and sometimes a scruffy or unkempt coat. The excess thyroid hormone speeds up nearly every system in the body, increasing blood flow through the kidneys and driving up urine output.
Left untreated, hyperthyroidism can cause high blood pressure, which damages the eyes, kidneys, heart, and brain over time. The good news is that it’s highly treatable. Options range from daily medication to a one-time radioactive iodine treatment that cures the condition permanently in most cats. One important nuance: hyperthyroidism can actually mask underlying kidney disease by artificially boosting kidney function. Once the thyroid is treated, kidney values sometimes rise, so vets typically monitor kidney health closely during and after treatment.
Diabetes
Feline diabetes works similarly to type 2 diabetes in humans. When blood sugar rises above a certain threshold (around 250 to 300 mg/dL in cats), the kidneys can no longer reabsorb all the glucose, and it spills into the urine. That excess sugar pulls water along with it, producing large volumes of urine and intense thirst. Classic signs include drinking and urinating much more than normal, increased appetite, and weight loss, especially loss of muscle along the spine and hind legs.
Overweight and inactive cats are at higher risk. Unlike dogs, some cats can actually go into remission with early, aggressive treatment and dietary changes, particularly a switch to high-protein, low-carbohydrate food. The earlier diabetes is caught, the better the chances of remission.
Less Common Causes
While the three conditions above account for most cases, a few other possibilities exist. Elevated calcium levels in the blood (hypercalcemia) can drive excessive thirst by affecting the kidneys’ ability to retain water. In cats, hypercalcemia sometimes has no identifiable cause at all, a situation vets call idiopathic hypercalcemia, which is unique to the species. It can also be linked to cancer, particularly lymphoma.
Urinary tract infections are relatively uncommon in cats overall, but the rate climbs to about 10 percent in cats over 10 years old. These infections can increase thirst and urination, and they sometimes develop secondary to another condition like diabetes or kidney disease rather than on their own. Liver disease and certain medications (particularly corticosteroids) can also trigger increased drinking, though these are less frequent culprits.
What Happens at the Vet
If you bring your cat in for increased thirst, expect a straightforward workup. The standard starting point includes a blood panel, a urinalysis, and a thyroid hormone level. Together, these three tests can identify or rule out kidney disease, diabetes, and hyperthyroidism in a single visit. The urinalysis is particularly telling: the concentration of your cat’s urine reveals a lot about how well the kidneys are functioning, sometimes before blood values show any abnormality.
Your vet will also likely check blood pressure, since hypertension accompanies several of the conditions that cause excessive thirst. If initial results are inconclusive, additional steps might include a urine culture to check for infection, imaging like an abdominal ultrasound, or the SDMA test to catch early kidney changes.
Most of these conditions are very manageable when caught early. The combination of increased thirst and increased urination in a senior cat is one of the clearest signals that something is shifting internally, and it’s one of the most productive reasons to get blood work done. Many owners look back and realize the water bowl had been emptying faster for weeks or months before they consciously registered the change.