Reference Values and Determinants of Hydration in Children 3-13 y

INCLUSION CRITERIA: * Boys and girls aged 3-13 years old * Parent willing to participate as a subject as well * Parents: aged 20-50 * Children and parents willing to collect urine samples and store them at room temperature * Avoid strenuous exercise on day of collection * Parent: included if \>50% of grocery shopping, food preparation, and feeding is handled by this parent EXCLUSION CRITERIA: Parents \& Children: * Evidence of clinically relevant metabolic, cardiovascular, hematologic, hepatic, gastrointestinal, renal, pulmonary, endocrine or psychiatric history of disease, based on the medical history questionnaire * Use of medication that interferes with water metabolism * Surgical operation on digestive tract (e.g. bariatric surgery), except possible appendectomy * Regular drug treatment within 15 days prior to start of the study * Not willing to refrain from exercise on the day before and during urine collection * Unwilling to collect urine * Inability to participate in the entire study * Pregnancy for females Children: * Use of Diapers * Enuresis or use of nappies during the day or during the night