Children's bodies have a higher percentage of water than those of adults, their metabolic rates are higher and they are at greater risk of infections that cause vomiting and diarrhoea. They are also dependent on others to feed them and give them water.
Older people may have a decreased thirst sensation, their kidneys may not work as efficiently or they may have neurological conditions such as a stroke or Alzheimer's disease, which can make it difficult for them to convey their needs to a caregiver. Incontinence problems may also lead elderly people to limit their intake of water.
Sports people who partake in strenuous sporting activities are also at risk of dehydration, particularly in very hot conditions.