As temperatures rise, public health campaigns urge people to drink more water. However, consuming excessive amounts can lead to overhydration, also known as water intoxication or hyponatraemia. Nurse Kelly Fisher, clinical health and wellbeing educator at Benenden Health, explains the risks and warning signs.
What happens when you drink too much water?
Electrolytes such as sodium, potassium, and calcium regulate nerve signals, muscle contractions, and hydration. Drinking more water than the body can process dilutes these electrolytes, causing a chemical imbalance. If sodium levels fall too low, water moves into cells, leading to symptoms from mild headaches to seizures or death in rare cases.
Key signs of overhydration
Fisher highlights urine colour as a key indicator. Clear urine suggests overhydration, while pale yellow indicates good hydration. Other early symptoms include nausea, vomiting, diarrhoea, headaches, muscle cramps, swelling, bloating, and fatigue. Severe confusion, seizures, difficulty staying awake, or loss of consciousness require immediate medical attention.
How much water do you actually need?
The British Dietetic Association recommends 1.5-2 litres of fluid daily (about 8-10 drinks). In hot weather, Wendy Lee, deputy superintendent at Well Pharmacy, advises adults to drink 2.5-3 litres daily to replace fluids lost through sweating. However, she warns not to exceed 1.5 litres per hour, as this can dangerously lower blood salt levels.
Tips for safe hydration
Listen to your body's thirst cues and sip fluids gradually. Adjust intake based on activity and environment—outdoor exercise in heat requires more water than resting at home. Boost electrolytes naturally with foods like spinach, nuts, bananas, and avocados. Electrolyte supplements are generally unnecessary for most people with a balanced diet. If symptoms like persistent nausea, headaches, swelling, or confusion occur, seek medical advice.
