Excessive thirst is a common symptom among both adults and children. Short-term acute thirst may signal nothing more than a hot day and a hard workout, or perhaps an oncoming viral or bacterial infection. Other times, especially if a child drinks a lot of water over a lengthy period of time, it can be a sign of something more serious. Many conditions causing excessive thirst in children are very serious and even life-threatening.
Children aged 4 to 8 need about 1.3 liters of water intake a day -- this includes the water content of food and other beverages as well as plain drinking water -- while kids age 9 to 13 need 2.1 to 2.4 liters a day. If your child is drinking more than this, consult his pediatrician, especially if the excessive intake lasts more than a day or two.
Excessive thirst is one of the key symptoms of diabetes mellitus. Diabetes mellitus comes in two forms, known as Type 1 and Type 2. Type 1 diabetes occurs when the pancreas stops producing insulin, while Type 2 occurs when the body is resistant to the effects of insulin. Type 1 is more common among children. Other symptoms of diabetes mellitus include frequent urination -- bedwetting and potty training relapses are a red flag -- fatigue, weight loss, increased appetite, sweet-smelling breath and sometimes vomiting, nausea and stomach pain. Diabetes mellitus is a serious condition that requires a doctor's close supervision to treat properly.
Diabetes insipidus shares a name with diabetes mellitus but is otherwise unrelated. It is also much rarer. Diabetes insipidus is caused when the body produces too little of the hormone known as antidiuretic hormone or ADH, which regulates the production of urine. Diabetes insipidus is marked by a prodigious output of urine, often between 4 and 10 liters a day. Other symptoms may include weight loss, dry skin and cool hands and feet.
An acute bout of excessive thirst may signal simple dehydration in a child. The dehydration could be caused by a number of factors, including excessive vomiting or diarrhea due to an infection, heat exhaustion or as a side effect of a medication such as a decongestant. Still, dehydration can be serious and if your child cannot keep fluids down due to vomiting or if she shows other signs of serious dehydration such as dark urine, lack of urine, or dry skin with no spring when pinched, see a doctor immediately.
Excessive thirst in a child can also indicate an underlying kidney disorder, as it is the kidneys' function to regulate fluid intake and urine output. Your child could be suffering from a rare form of genetic polycystic kidney disease, which can cause blood in the urine and high blood pressure as well as excessive thirst. Other possibilities include rare forms of cancer, childhood nephrotic syndrome or incipient kidney failure due to other untreated conditions.