Dry mouth and dehydration: what should you know?

Dry mouth can signal dehydration, especially with thirst, dark urine, dizziness, tiredness or reduced urination. Fluid loss from vomiting, diarrhoea, heat or heavy sweating can reduce saliva and concentrate urine. Dryness alone is not proof of dehydration because medicines, mouth breathing and some illnesses can affect saliva too.

Gastroenteritis may remove fluid through vomiting or diarrhoea. Heat exhaustion and strenuous activity can increase losses through sweat. Dark urine and constipation can occur when the body has less available water, while cloudy urine has several possible causes and should not be interpreted alone. Kidney stones and urinary tract infection can cause urinary symptoms or pain, but dry mouth does not diagnose either condition. Consider how much you have drunk and what fluid you may have lost.

Move to a cool place, rest and take frequent small sips of water. After vomiting or diarrhoea, an oral rehydration solution may replace water and salts; follow the product instructions. Continue suitable food when able, and avoid alcohol. Do not force large amounts quickly if you feel nauseated. A pharmacist or clinician can advise about fluid replacement if you have kidney, heart or liver disease, or have been told to restrict fluids.

Seek emergency help for confusion, fainting, severe weakness, inability to keep fluids down, very little urine, or signs of heat illness with altered behaviour. Arrange prompt assessment for ongoing vomiting or diarrhoea, severe abdominal or flank pain, painful urination, or dehydration that does not improve with drinking. Children, older adults and people with chronic illness may deteriorate sooner.

Do my symptoms fit dehydration or could a medicine be reducing saliva? Which rehydration drink is suitable for me? Should my urine, kidney function or electrolytes be checked? How much should I drink if I have a fluid restriction?