Experienced and professional animal trainer provide their insights in answering this question :
A. It may just be normal for your dog, also some diets are a lot drier than others which means they will drink more. But it could also be due to infection or a medical problem such as diabetes. I would recommend having a vet check first to rule out any medical concerns.

How to Identify Common Pet Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced pet care professionals :

Some common causes of a dog suddenly drinking a lot more water include kidney failure, diabetes mellitus, Cushing`s disease, or simply dehydration, all of which need to be addressed. If you notice your senior dog is drinking more water than usual, plan a visit to the vet.
But is it possible for your dog to drink too much water? As important as it is to avoid dehydration, there can be too much of a good thing. Many owners — and even some veterinarians — are unaware that an overabundance of water in a dog`s system can lead to frightening symptoms and even death.
When dogs become stressed or anxious, they will often pant and sweat more, causing greater loss of water than just through urination. To replace the fluids they lack, they will drink more water. A stressed dog may also urinate inappropriately.
Why Is My Dog Drinking Lots of Water and Licking Their Paws? These signs together can be caused by dehydration, allergies, pain, or even behavioral issues, including anxiety, stress, or cognitive dysfunction (the dog version of dementia).
Glomerulonephropathy is an inherited disease that slowly damages your Shih Tzu`s kidneys, causing them to fail, often at an early age. Because damaged kidneys leak protein, we may be able to diagnose this disease by annually testing your pet`s urine for excessive protein.
Hyperadrenocorticism (Cushing`s)

Cushing`s Disease is a malfunction of the adrenal glands that causes them to produce too much steroid hormone. This is a common problem in dogs, and your Shih Tzu is more likely than other dogs to be affected. The condition usually develops slowly, and the early signs are easily missed.

Addison`s disease in dogs (also called hypoadrenocorticism) occurs when your dog`s adrenal glands aren`t producing adequate levels of corticosteroid hormones. If diagnosed and treated appropriately these dogs can live a long, happy life. The adrenal glands are two small glands next to the kidneys.
Dogs have several reasons for staring at their owners, like to communicate with and understand us. Some dogs stare to manipulate owners, as in with begging for food or asking to be let outside. Training and dog sports are good ways to turn focused staring behavior into a positive experience.
Signs That Your Dog May Have a UTI

If your canine companion has a UTI you may notice one or more of the following symptoms: Frequent urination. Excessive thirst. Accidents in the house.

A general rule of thumb for determining the amount of water a dog should drink daily is 1 ounce (1/8 of a cup) of fluids per pound of body weight. For example, a 10-pound dog should drink approximately 10 fluid ounces per day, while a 100-pound dog should drink roughly 100 fluid ounces in a day.
When kidneys are failing, the increased concentration and accumulation of substances in urine lead to a darker color which may be brown, red or purple. The color change is due to abnormal protein or sugar, high levels of red and white blood cells, and high numbers of tube-shaped particles called cellular casts.
There is a higher prevalence of pancreatitis in Miniature Schnauzers, Yorkshire Terriers, Cocker Spaniels, Dachshunds, Poodles, sled dogs, or other breeds. Some infections, such as Babesia canis or Leishmania, may also contribute to the development of pancreatitis.
Gastritis is defined as inflammation of the lining of the stomach. It may occur as a short episode (acute) or have a long duration (chronic) and may be associated with underlying conditions that are more serious.
In the first stage of Renal Dysplasia, there is a silent and progressive decrease in kidney function over months, or even years. During stage two, the kidneys are working at about 30% efficiency and symptoms become obvious: Excessive thirst, high volume of pale urine, loss of weight, low energy.
The number one cause of death for Shih Tzu dogs is old age and complications due to this. The second most common cause of death is heart conditions which can be heart attacks and heart failures. The third most common cause of death for Shih Tzus is acute and chronic kidney failure.
If your dog`s appetite, hydration, hygiene, skin health, and sleep are all affected, the quality of life has dramatically decreased due to Cushing`s disease. At that point (or even before) it may be time to consider euthanasia as the kindest decision.
Cushing`s disease (hyperadrenocorticism) is a serious health condition in dogs that occurs when the adrenal glands overproduce cortisol (cortisone) in the animal`s body. Excess cortisol can put a dog at risk of several serious conditions and illnesses, from kidney damage to diabetes, and can be life-threatening.
Addisonians may be misdiagnosed with gastrointestinal disease, dehydration, kidney disease, pancreatitis, a ruptured bladder, or certain types of poisonings. The only way to definitively diagnose Addison`s disease is through an ACTH stimulation test.
Lethargy, weakness, vomiting, diarrhea, and/or poor appetite are common signs. A marked increase in thirst and urination is often noted in the days to weeks before diagnosis, and dogs can become dehydrated. Some dogs present in shock or for collapse; this is called an Addisonian crisis.
Its onset can be sudden and severe, or it may only flair up intermittently and its intensity will vary from episode to episode. Stress is a culprit for triggering Addison`s disease in dogs, but not the only cause. A pet`s personality plays a factor in how stress is managed.
Signs of muscle and joint pain, nervousness, and depression are also common in dogs with Addison`s disease. When a dog is under duress, the body produces cortisol, so without a normal level of this hormone, clinical signs can worsen.
A third common cause of stomach swelling in dogs is hyperadrenocorticism, or Cushing`s syndrome. If your dog has Cushing`s, he will have a pot-bellied look along with increased hunger, thirst, and urination. Some dogs will also start to lose hair or show an increase in panting.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Q. My dog drinks a lot of water, should I worry?
ANSWER : A. Firstly, you should quantify if your dog is actually drinking an excessive amount of water. In a 24 hour period, a dog should drink about 1 fluid ounce (or 30mL) per pound of body weight. Therefore, the recommended amount of water intake (in fluid ounces) equals your dog’s weight (in pounds). For example, if your dog weighs 8 pounds, he/she should drink about a cup of water in a 1 hour period. This will be slightly increased if your dog gets a lot of physical activity or lives outdoors.

You can measure your dog’s water intake the following way: in the morning, measure a specific amount, a little bit more than you think he/she will drink. 24 hours later, measure the remaining amount. If the amount of water your dog drank is significantly greater than it should be, then you should take your dog to a veterinarian.

Causes for mildly increased water consumption include: food changes, increased ambient and body temperature, increased activity, urinary tract infection, and general illness.

Common causes for greatly increased water consumption include: diabetes, urinary tract infection, kidney disease, steroid use, and other systemic diseases. With large increases in water consumption, you will also usually see increased urination. Please take note of urinary patterns to discuss with your vet. Greatly increased drinking and urination is ALWAYS a reason to see a vet.

Q. Why would my Shih Tzu drink tremendous amounts of water everyday ?
ANSWER : A. It may just be normal for your dog, also some diets are a lot drier than others which means they will drink more. But it could also be due to infection or a medical problem such as diabetes. I would recommend having a vet check first to rule out any medical concerns.

Q. Why doesn’t my weenie dog ever drink hardly any water?
ANSWER : A. On average dogs should consume about 70 – 100 milliliters of water per kilogram of body weight per day. Measure your dog’s water consumption over a 24 hour period to see if he’s consuming appropriate amounts. You can add canned food to his diet – it’s high in water content, about 70%. Also adding a very small amount of low sodium chicken broth to his water bowl might encourage him to drink more.

Q. My dog just puked on the tile and layer around. He then proceeded to get up and drink 4 bowls of water. Why did he drink so much water?
ANSWER : A. He was feeling thirsty because he has lost lots of fluids with the vomit and his body was telling him to increase the water intake. It’s normally a good idea to start offering small amounts of water little and often, otherways if the stomach is still upset, too much water can cause the vomiting to occurr again.

Read Full Q/A … : Vetinfo

Q. My dog keeps drinking water and then throwing it back up
ANSWER : A. I would recommend to limit the amount of water that your dog is drinking, otherwise will keep vomiting. The plan of action would depend on the cause of vomiting, but generally speaking it is wise to starve your dog for next 8-12hours and then start again feeding with a bland diet based on boiled chicken and rice. Give small portions of food every 3-4 hours. If the vomit continues despite starvation, I would strongly recommend to take your dog to your veterinarian for a check up and appropriate treatment. Please engage in a consultation if you require further advices

Q. My dog throws up after drinking water, what should I do?
ANSWER : A. If this only happens occasionally (a few times per week or month), and your dog throws up just water, it is not usually an emergency. Consider your dog’s activity before the event – physical activity, stress, elevated temperature, drinking too fast, and inhaling water can cause them to vomit water. Try elevating the bowl, giving him/her small amounts of water at once and waiting a few minutes after the activity.

Even if this has only happened once, if your dog is acting strange afterwards (low level of activity, not eating, etc.) you should visit your veterinarian immediately. Vomiting can be a sign of an obstruction, heat stroke, or a multitude of other causes.

If this happens frequently and you cannot figure out the cause, your dog should also be examined by a veterinarian. Chronic daily vomiting can be a sign of many problems, including a chronic obstruction, other gastrointestinal disease, or a systemic disease.

Q. Dog six months has stop eating and drinking all together for five days now. Vet says not to worry. She ribs are starting to show what could be wrong?
ANSWER : A. I would be worried. Not eating or drinking… Step one is to figure out why, step two is change in food to encourage weight gain. I would recommend a good physical exam by a veterinarian, and some abdominal radiographs to rule out an obstruction. Given that it has now been 6 days, I would recommend hospitalized supportive care. IV fluids, plasma if available, and antibiotics if indicated. In regards to nutrition, high calorie food such as Hills a/d will help, but once recovered I would simply put on a high quality puppy food such as Acana, Orijen, lotus, honest kitchen etc. Human grade ingredients with less additives. Best of luck. If you would like to consult and discuss in further detail, I would be happy to help.

Q. Can I give my dog ice water to drink?
ANSWER : A. Yes, of course you can. However, you do not want to give ice water to your dog when he is already overheating. If your dog is panting, shallow breaths, vomiting, displaying gums of a different color, having diarrhea, or lethargic, do not give him ice water. Ice, ice water, and very cold water all shock your dogs system, and constrict the blood vessels, making your dog hotter in-turn. It could turn deadly.

If your dog is acting normal, and in a cool room, feel free to give him some ice water, or ice cubes! There a fun treat, and you have nothing to worry about. It’s truly only when they’re very hot, or overheating.

FYI, if the dogs are vomiting, panting with shallow breaths, having diarrhea, etc.. please see a vet immediately.