NDI renders the kidneys unable to reabsorb the body water flowing through their collecting ducts by disrupting their ability to balance body water. Body water that should be reabsorbed is instead voided as dilute urine. This could lead to severe dehydration, which is a life-threatening condition. Fortunately, all that is needed to prevent dehydration is ready and reliable access to water. This may require careful planning for youngsters, but it is definitely doable.

Infants born with NDI begin to manifest its symptoms in the first days of life. NDI's two primary symptoms, polyuria and polydipsia, can be difficult to detect in an infant, and the NDI infant cannot communicate his increased need for water in words. But there are other symptoms that can alert the parent or caregiver to the possibility that their infant may have NDI and therefore need much more water intake than normal.

The NDI infant may be irritable, feverish, or constipated. He or she may fail to thrive, vomit often, be anorexic, and prefer water to milk. Should the infant's polyuria go unnoticed and untreated, he or she may suffer severe bouts of dehydration, which result in excessively high plasma sodium levels. This could cause mental and physical retardation, and even death. Extreme as these conditions are, Dr. Bichet, one of the world's leading NDI researchers and treatment specialists, has observed that as long as the NDI infant has adequate and timely access to water, he or she can experience normal development and a normal life span.

Elderly people with NDI also require careful monitoring. They may not be able to communicate their need for water either. And sometimes they become less sensitive to their thirst. Elderly patients suffering from dehydration can be more prone to infection, kidney failure, confusion, lethargy, constipation and decreased skin turgor.

Whether the patient is an infant or an elderly person, clinicians can check the patient's plasma sodium level. If it is abnormally high, it may indicate dehydration.