Tracking Appetite and Thirst: The Two Numbers That Change First

Ask a vet what they most wish owners could tell them accurately, and appetite and water intake come up constantly.

Both change early in a huge range of diseases. Both are things owners think they know and usually don't, because "he's eating fine" and "he drinks normally" are impressions rather than measurements — and impressions drift.

Why guessing fails

Free-feeding. If the bowl is topped up whenever it's empty, nobody knows the actual daily amount.

Multiple people feeding. In a household of three, everyone assumes someone else fed the dog, or two people both did.

Multiple pets. Whose water bowl is that? Who ate what?

Gradual change. A cat drinking 20% more than last month is not perceptible. A cat drinking twice as much might be, eventually.

Outdoor access. Cats and dogs who drink outside, from ponds, taps or a neighbour's bowl.

The fix in each case is to measure once, properly, so you have a real number to compare against.

Measuring food intake

Once, do it properly:

1. Weigh the day's food on a kitchen scale rather than using a scoop. Scoops vary enormously — a "cup" of one kibble weighs very differently from another.

2. Record the amount offered.

3. At the end of the day, weigh what's left.

4. Subtract.

That's their normal daily intake, in grams. Write it down.

Then track changes, not absolutes. You don't need to weigh every meal forever. You need to know the normal figure so that when you suspect a change, you can measure again and compare.

Practical notes:

Include treats in your mental accounting. They're frequently 20–30% of a dog's calories and owners rarely count them.
Feed measured meals rather than free-feeding, for dogs especially. It gives you daily information for free — you see immediately when a meal isn't finished.
In multi-pet homes, feed separately. It's better for monitoring and reduces competition-related stress.

What matters:

A meal refused is worth noting, not panicking about
Two consecutive meals refused in a dog — call the vet
24 hours of not eating in a cat — vet, same day. Cats can develop hepatic lipidosis from short periods of not eating. This is genuinely urgent and not an overreaction.
Gradual decline over weeks — often more significant than a sudden refusal, and much easier to miss
Increased appetite with weight loss — a classic combination pointing to hyperthyroidism in cats, or diabetes, or malabsorption. Very important and often mistaken for a good sign.

Measuring water intake

This is the one that catches serious disease earliest, particularly in cats.

The method:

1. Measure water into the bowl with a jug. Note the volume.

2. Record any top-ups during the day.

3. Exactly 24 hours later, measure what's left.

4. Subtract to get intake.

Corrections:

Evaporation matters on hot days. Put an identical bowl of measured water somewhere the pet can't reach and measure its loss over the same period. Subtract that.
Restrict other sources for the test period — close the toilet lid, keep them indoors, remove other bowls or account for them.
Separate pets if possible.

The numbers:

Normal is roughly 40–60ml per kilogram per day from all sources.

Diet changes this enormously. Wet food is 75–80% water, dry food around 10%. A cat on wet food may drink almost nothing from the bowl and be perfectly hydrated. The same cat on dry food might drink 150–200ml. Both are normal.

The threshold that matters regardless of diet: more than 100ml per kg per day is abnormal. For a 4kg cat that's 400ml; for a 20kg dog, 2 litres.

But more useful than any absolute is change against their own baseline. A cat that used to drink 80ml and now drinks 200ml needs investigating even though 200ml isn't a dramatic figure in isolation.

What increased thirst means

Increased drinking, and the increased urination that goes with it, is one of the most important signs in veterinary medicine:

Chronic kidney disease — the commonest cause in older cats
Diabetes mellitus
Hyperthyroidism in cats
Cushing's disease in dogs
Liver disease
Uterine infection (pyometra) in unspayed females — an emergency
High blood calcium, sometimes associated with certain cancers
Some medications, particularly steroids and diuretics

Almost all of these are diagnosed with a blood test and urine test. Several are very treatable if caught early.

What decreased thirst means

Less common but also significant — usually a sign of nausea or general malaise. A pet who has stopped drinking is at real risk of dehydration and needs to be seen.

The proxy measures

If measuring is impractical, these are useful stand-ins:

For cats: the litter tray. You're handling the evidence daily. Note how many clumps and how big. A tray suddenly needing changing twice as often is a real signal. This is one of the strongest arguments for keeping an indoor tray even for cats with outdoor access.

For dogs: how often they ask to go out, and whether there are overnight accidents in a previously reliable dog. Both are meaningful.

Bowl refills. If you normally refill a 1-litre bowl every two days and you're now doing it daily, that's a doubling.

How often to check

Healthy adult: measure water intake once to establish baseline, then re-measure every few months or any time you have a suspicion
Senior pet: every month or two
Diagnosed kidney disease, diabetes or hyperthyroidism: as your vet advises, often weekly

Food intake is easier — feeding measured meals means you monitor it continuously without effort.

Taking it to the vet

The difference this makes in a consultation is substantial.

*"He's been drinking a bit more I think"* is a starting point.

*"He was drinking about 700ml a day in March, and this week he's on 1.6 litres. His weight has dropped from 24kg to 22.3kg over the same period, and his appetite has increased."* — that's a near-complete clinical picture pointing in a specific direction, before anyone has drawn blood.

Our community tracker logs food and water intake alongside weight and prompts when a trend moves, which is the point — these numbers only ever mean something in comparison to what they were before.