Dehydration in Dogs: Signs, Causes and What To Do

Dogs lose water all day, every day — panting, playing, digesting food, just existing. Normally they top it back up by eating and drinking without you having to think about it. But when they lose more fluid than they take in, dehydration sets in, and it can go from “keep an eye on it” to genuinely serious faster than most owners expect.

The good news is that dehydration is one of the most preventable health issues your dog will ever face. Once you know the causes, the signs, and a couple of quick checks you can do at home, you’ll rarely be caught out.

Why water matters more than you’d think

It’s easy to assume water is just about quenching thirst, but it’s doing far more work than that behind the scenes. It regulates your dog’s body temperature, keeps digestion moving, helps transport nutrients around the body, and — often overlooked — cushions the joints by keeping the fluid inside them properly lubricated. A dog that’s chronically under-hydrated isn’t just thirstier; their joints, gut and organs are all working harder than they should.

What causes dehydration in dogs?

Not drinking enough. This is the most common cause by far. It might be as simple as an empty water bowl, or a dog who’s feeling under the weather and has gone off drinking along with everything else.

Excess fluid loss. Long walks, hot weather, and heavy panting all increase how much water your dog loses. On warm days, or after exercise, they’ll need noticeably more than usual to keep up.

Vomiting and diarrhoea. These can drain fluid from your dog’s system surprisingly quickly — often faster than reduced drinking alone. A dog with an upset stomach is at real risk of dehydration within hours, not days.

Underlying health conditions. Diabetes, kidney disease and some infections can all affect how a dog manages water balance. If dehydration keeps recurring without an obvious cause, it’s worth a proper vet check to rule these out.

Age. Senior dogs are more prone to dehydration — their kidneys are often less efficient at conserving water, and conditions common in older age (reduced appetite, joint pain that puts them off getting up for water, kidney changes) can all make it worse. If you’re caring for an older dog, our complete guide to senior dog health covers the wider picture of what to watch for as they age.

Signs of dehydration in dogs

Some of these appear early, others only once dehydration has progressed — so don’t wait for every box to be ticked before taking action.

• Dry or tacky gums
• Thick, sticky saliva
• Lethargy or reluctance to move
• Loss of appetite
• Sunken-looking eyes
• Excessive panting
• Loss of skin elasticity (see the test below)
• Increased heart rate
• Vomiting
• Noticeably darker urine, or less of it than usual

The 60-second test you can do at home

This is the one thing the guides on this topic tend to skip over — but it’s genuinely useful, and it takes seconds:

The skin tent test. Gently pinch a bit of loose skin between your dog’s shoulder blades and lift it up, then let go. In a well-hydrated dog, it should spring back flat almost instantly. If it drops back slowly, or stays “tented” for a moment, that’s a sign of reduced skin elasticity — a classic marker of dehydration.

The gum check. Press a fingertip gently against your dog’s gum, then release. Healthy gums should return to their normal pink colour within about 1–2 seconds. If it takes noticeably longer, or the gums feel dry or tacky rather than slick, that also points to dehydration.

Neither test replaces a vet visit if you’re worried, but they’re a quick, reliable gut-check while you decide what to do next.

What to do if you think your dog is dehydrated

Contact your vet for guidance, especially if your dog seems unwell alongside the dehydration. While you wait to speak to them:

• Offer small amounts of water frequently rather than letting them gulp a large bowlful — drinking too much too fast can trigger vomiting and make things worse
• Try a dog-safe electrolyte solution if your vet recommends one — never give a human rehydration product without checking first, as some contain ingredients or sugar levels unsuitable for dogs
• Offer wet or moisture-rich food if they’re willing to eat
• Move them somewhere cool and shaded straight away if overheating is part of the picture — heat and dehydration make each other worse
• Keep them calm and quiet rather than continuing exercise or play

When it’s an emergency

Get to a vet immediately — don’t wait it out at home — if your dog is showing any of the following alongside dehydration:

• Collapse, extreme lethargy, or unresponsiveness
• Repeated vomiting or ongoing diarrhoea
• Signs of heatstroke (heavy panting, drooling, bright red gums, disorientation)
• Refusing water entirely for several hours
• Known or suspected underlying illness

Dehydration can escalate quickly, particularly in puppies, senior dogs, and smaller breeds, so it’s always better to call your vet than to wait and see.

Dehydration from an upset tummy

Because vomiting and diarrhoea are such a common route to dehydration, keeping your dog’s digestion settled is one of the more practical things you can do to reduce the risk in the first place. A gut that’s producing firm, well-formed stools loses far less fluid than one dealing with ongoing loose motions. Our Enhanced Dog Probiotics for Digestive Health is designed to support exactly that — a simple powder added to food that helps maintain healthy gut balance and firmer, more consistent stools, particularly useful for dogs who are prone to tummy upsets.

Hydration and healthy joints

It’s easy to forget that water is a structural part of your dog’s joints, not just something they drink. Synovial fluid — the natural lubricant inside every joint — relies on good hydration to stay effective at cushioning movement. A dog that’s chronically borderline dehydrated is putting extra, avoidable strain on joints that may already be working hard, especially in adult and senior dogs. Alongside making sure fresh water is always available, our range of joint supplements — including our Senior Dog Joint Chews and Senior Max Plus High Strength formula — are enhanced with turmeric to support joint comfort as part of a broader hydration and mobility routine.

Preventing dehydration in dogs

• Keep fresh water available at all times, at home and out and about
• Pack water for both of you on longer walks or day trips
• Avoid exercising during the hottest part of the day
• Watch water intake more closely during warm weather, illness, or after vomiting/diarrhoea
• Keep an eye on senior dogs and small breeds especially, as they’re more vulnerable

For a full breakdown of keeping dogs safe in warm weather, our guide on how to cool down a dog in hot weather covers this in more depth.

FAQs

How much water does a dog need each day?

As a rough guide, most dogs need around 50ml of water per kg of body weight per day — so a 20kg dog needs roughly 1 litre. This varies with activity level, diet (wet food contributes moisture too), weather, and individual dogs, so treat it as a starting point rather than a strict rule.

Can I give my dog Dioralyte or a human rehydration sachet?

Not without checking with your vet first. Some human electrolyte products contain sugar levels, flavourings or sodium concentrations that aren’t appropriate for dogs. Dog-specific electrolyte solutions are the safer choice, and your vet can recommend one if needed.

How quickly can a dog become dehydrated?

Faster than most owners expect — particularly with vomiting or diarrhoea, or in hot weather with heavy panting. A dog can go from fine to noticeably dehydrated within a matter of hours in the wrong conditions, which is why early signs are worth acting on rather than waiting to see if they pass.

Are some dogs more at risk of dehydration than others?

Yes. Senior dogs, puppies, flat-faced (brachycephalic) breeds, and dogs with underlying health conditions like kidney disease or diabetes are all at higher risk and worth monitoring more closely, especially in warm weather.

The bottom line

Dehydration is common, usually preventable, and — caught early — straightforward to put right. Keep fresh water available, know the signs, use the skin tent and gum tests if you’re ever unsure, and don’t hesitate to call your vet if something doesn’t look right. A little vigilance goes a long way toward keeping your dog comfortable, hydrated and happy.

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Browse our natural dog supplements or read more advice over on the Canine Life Co. blog.

The information in this article is for general guidance only and isn’t a substitute for professional veterinary advice. If you’re worried about your dog’s health, please contact your vet.