First, be sure the increase is real and sustained
Dogs drink more on hot days, after salty chews, after vigorous exercise, and when a household routine changes — a new bowl position, more people at home refilling, or a second dog visiting can all make a water bowl empty faster without your dog's thirst changing at all. A genuine increase is one you can verify: the bowl needs refilling far more often across several ordinary days, your dog seeks water at unusual times, drinks from puddles or taps he previously ignored, or wakes at night to drink.
Measuring settles the argument. Fill the bowl with a known amount in the morning, top up by measured amounts, and note what remains the next morning for a couple of days. Those figures are far more useful to a vet than saying he seems thirstier.
Why vets investigate increased thirst rather than watching it
Sustained heavy drinking is rarely a habit; it is usually the visible end of the body losing or needing more water, and the underlying reasons range across kidneys, hormones, infection, and other internal conditions that an owner cannot distinguish at home. That is why the standard response to a confirmed, unexplained increase is an examination with tests rather than a period of waiting to see if it passes.
The company it keeps sharpens the urgency. Drinking more plus urinating more, including night-time accidents in a reliably house-trained dog, losing weight while eating normally or hungrily, a dull coat, vomiting, or fading energy should be booked promptly and described as a set, not as thirst alone.
What not to do while you wait for the appointment
Never restrict or ration your dog's water to reduce the urinating or test whether he really needs it. A dog drinking heavily usually needs that water, and limiting it can make him unwell quickly, especially in warm weather. Instead, make access easy — water in the rooms he uses, a top-up before bed, and more garden trips or a night-time let-out so he is not distressed trying to hold on.
Also note any new foods, chews, or changes at home, and whether other dogs in the house are drinking normally from the same supply, because those comparisons help the vet judge whether this is one dog's change or a household artefact.
What to bring to the visit
Bring your measured intake figures, notes on urination changes and accidents, appetite and weight observations, and a fresh urine sample if your vet's reception team asks you to collect one — catching it in a clean shallow container on the morning walk is usually easiest. Ask what the tests are looking for and when results will be discussed, so the waiting period has a shape.
Look at the whole dog alongside the bowl: a coat that has lost its shine, a waistline shrinking under a normal appetite, or a dog who asks to go out far more often at night tells the same story from different angles and strengthens the case you describe. Keep a note of toilet trips for a couple of nights if you can, without turning the house upside down — even rough counts help. If you use an automatic water dispenser, switch temporarily to a measured bowl, because a dispenser hides exactly the change you are trying to prove.
Entering the intake measurements, test results, and follow-up plan in KinsLe Pet Passport keeps the whole investigation together if monitoring continues over later visits.