Both drinking too little and, more rarely, drinking too much water can cause real problems. Here's how to recognise the signs of each, a simple urine colour guide, who's most at risk, and when it's time to see a doctor.
Mild dehydration typically shows up as thirst, a dry mouth, dark yellow urine, headache, tiredness and slightly reduced urine output. These are your body's earliest warning signs, and they usually resolve quickly once you drink fluids.
| Severity | Common signs |
|---|---|
| Mild | Thirst, dry mouth, dark yellow urine, mild headache, tiredness |
| Moderate | Dizziness, reduced urine output, dry skin, rapid heartbeat, confusion in some cases |
| Severe (seek urgent care) | Very little or no urination, sunken eyes, rapid breathing, extreme confusion, fainting |
Get a personalised daily water intake target based on your body weight, activity and climate.
Open the Water Intake Calculator →Urine colour is one of the simplest everyday indicators of hydration status, though it isn't perfectly precise — some vitamins, medications and foods can temporarily change urine colour regardless of hydration.
| Urine colour | Likely meaning |
|---|---|
| Pale straw / light yellow | Generally indicates good hydration |
| Clear / very pale | You may be drinking more fluid than you need — not usually a concern on its own |
| Dark yellow | Possible mild dehydration — drink more fluids |
| Amber or honey-coloured | Likely dehydrated — increase fluid intake |
| Brown, red, or unusual colour | Not a hydration sign — could indicate a medical issue; see a doctor |
Yes, though it's uncommon in everyday life. Drinking far more water than your kidneys can excrete — particularly in a short period — can dilute the sodium concentration in your blood, a condition called hyponatremia, sometimes referred to as water intoxication. In serious cases this can be dangerous.
| Severity | Common signs |
|---|---|
| Mild | Nausea, bloating, feeling "sloshy" |
| Moderate | Headache, vomiting, confusion, fatigue |
| Severe (seek urgent care) | Confusion, seizures, loss of consciousness |
This is genuinely rare in typical daily drinking — healthy kidneys can process a substantial amount of water. It's more commonly reported in specific situations like endurance sports events (where athletes over-drink to try to prevent dehydration), certain psychiatric conditions involving compulsive drinking, or deliberate rapid over-consumption.
See a doctor promptly, or seek urgent care, if you or someone else has signs of severe dehydration (very little urination, sunken eyes, rapid breathing, extreme confusion, fainting) or signs of significant overhydration (confusion, seizures, loss of consciousness). For ongoing mild symptoms — persistent dark urine, frequent headaches, regular fatigue — it's still worth mentioning to your GP, particularly if adjusting your fluid intake doesn't resolve them.
What are the early signs of dehydration?
Early signs include thirst, a dry mouth, dark yellow urine, headache, tiredness and slightly reduced urine output. These are your body's early signals and usually resolve with fluids.
Can you drink too much water?
Yes, though it's uncommon in everyday life. Drinking far more water than your kidneys can process, especially in a short period, can dilute blood sodium levels (hyponatremia), which can be serious. This mainly happens with very rapid, excessive intake, such as during endurance events.
What colour should urine be if you're well hydrated?
Pale straw or light yellow urine generally indicates good hydration. Dark yellow or amber suggests you may need more fluids, while very pale or clear urine can occasionally indicate you're drinking more than you need.
Who is most at risk of dehydration?
Older adults (due to reduced thirst sensation), infants and young children, people who are unwell with vomiting, diarrhoea or fever, athletes and outdoor workers in hot conditions, and people on certain medications like diuretics are at higher risk.
Dehydration signs progress from thirst and dark urine (mild) through dizziness and confusion (moderate) to a medical emergency (severe). Overhydration is rarer but real, and can also become serious in extreme cases. Urine colour is a simple everyday guide for most healthy adults, and a personalised daily water target — adjusted for your body weight, activity and climate — is a practical way to stay ahead of both extremes.