A number of things can cause your puppy to drink excessively; some are harmful and some are not. Take your young dog to the vet for a checkup.
First, distinguish between excessive drinking and increased drinking. It's possible your puppy is drinking a lot, perhaps noticeably more than before, but not necessarily excessively. If she lost a source of fluids from a dietary change or has become more active, or if the summer heat set in, an increase in water consumption is perfectly normal. On average, your puppy should be drinking somewhere in the vicinity of 30 milliliters of water per pound of body weight daily. However, a number of individualized factors affect what's normal and healthy; talk to your vet about how much your puppy is drinking. She'll help you determine what's appropriate and what's excessive.
Sometimes, your puppy's food makes her drink more. Salty or sugary foods make dogs more thirsty, as do low-protein diets. Also, if your puppy is eating something containing an ingredient she's allergic or intolerant to, resulting symptoms -- such as odd throat sensations, diarrhea, or vomiting -- may prompt her to keep drinking. If your puppy doesn't like her food and isn't eating enough, she may try to fill up on water. Another consideration is whether you recently switched from canned food to dry kibble. If so, your puppy's gone from food that's 75 percent moisture to food that's 6 to 10 percent moisture; she may be making up the new deficit by drinking more.
Kidney and liver disease commonly cause significant thirst. These are life-threatening conditions that require veterinary attention, which is why it's so important to take your puppy in when you notice her drinking excessively. Diabetes, adrenal and thyroid dysfunction, certain cancers, hormonal imbalances, urinary tract infections, elevated blood calcium levels and other illnesses all sometimes cause polydipsia as a clinical sign. Dehydration also drives an animal to drink more. Occasionally, not the condition but the treatment is to blame. Many medications cause increased thirst as a side effect.
What to Do
See your vet, but don't restrict your puppy's access to water. If your vet determines your puppy drinks too much, he'll proceed with figuring out why. Obviously, the treatment depends entirely on -- and varies widely according to -- the underlying cause. If other symptoms point to a food allergy or intolerance, for example, your vet will design an exclusion diet to discover the problematic ingredient. Liver, kidney, adrenal or thyroid dysfunction are corrected or managed with appropriate therapies. Depending on what the symptoms, history and physical examination indicate, your puppy may need various tests, such as urinalysis, blood work, X-rays or others. The prognosis, like the treatment, depends on the diagnosis and sometimes how early in a disease's progression it was identified.