Dark urine and dehydration

The kidneys conserve water when the body has less fluid available, so urine becomes smaller in volume and deeper in colour. Dry mouth, thirst, headache, dizziness, constipation, tiredness, and a strong urine smell may occur alongside it. Gastroenteritis can cause rapid fluid loss, while heat exposure and heavy sweating can do the same. Dark urine is not a measurement of dehydration by itself: food, medicines, blood, infection, and liver conditions may alter colour. Pain in the side or groin can suggest a kidney stone, while burning and frequent urination can suggest a urinary tract problem.

Move to a cool place if heat contributed and take frequent small drinks. If vomiting or diarrhoea is present, ask a pharmacist or clinician whether an oral rehydration product is suitable. Continue light meals if tolerated, and monitor urine amount, dizziness, and alertness. Avoid relying on alcohol to replace fluid. People with heart, kidney, or other conditions affecting fluid balance should ask for individual guidance rather than forcing fluids.

Seek urgent help for confusion, fainting, severe weakness, inability to keep fluids down, very little or no urine, blood in urine, severe abdominal or flank pain, or signs of heat illness. Contact a clinician if dark urine does not improve as you recover or if fever and urinary symptoms develop.

Ask how much fluid is appropriate for you, whether you need urine testing, and whether vomiting, diarrhoea, constipation, heat exposure, or a medicine could be contributing.