As temperatures climb, reminders to drink more water are everywhere, from GP waiting rooms to public transport stations. Staying hydrated is crucial during a heatwave, helping the body regulate temperature and reducing the risk of dehydration and heat-related illness. However, excessive water consumption can lead to overhydration, also known as water intoxication, water poisoning, or hyperhydration. While far less common than dehydration, it is a dangerous condition.
What happens when you drink too much water?
Kelly Fisher, a nurse turned clinical health and wellbeing educator at Benenden Health, explains: 'Electrolytes are essential minerals, such as sodium, potassium, and calcium, which carry a positive or negative electrical charge when dissolved in bodily fluids like blood. They play a crucial role in regulating nerve signals, muscle contractions, and hydration levels to keep your heart, brain, and organs functioning properly.' Consuming more water than the body can process creates a chemical imbalance, diluting the bloodstream's electrolyte content. If sodium levels fall too low, a condition called hyponatraemia can develop, causing water to move into cells and leading to symptoms from mild headaches and nausea to seizures and loss of consciousness, or in rare instances, death.
Symptoms of water intoxication
Fisher says urine colour is a key indicator: 'Clear urine can be a sign that you are overhydrated, while a consistently pale-yellow urine colour can mean that you have good hydration levels.' Other common overhydration symptoms include nausea, vomiting, diarrhoea, headaches, muscle cramps, swelling, bloating, and fatigue. As sodium levels continue to fall, symptoms can become much more serious. Severe confusion, seizures, difficulty staying awake, or loss of consciousness are medical emergencies requiring immediate treatment.
How much water do you actually need?
The British Dietetic Association recommends adults drink around 1.5-2 litres of fluid daily, roughly 8-10 drinks (a typical mug or glass is about 200 millilitres). Fluid requirements depend on age, body size, activity levels, and overall health. Children need slightly less, around 6-8 drinks a day. Wendy Lee, deputy superintendent at Well Pharmacy, comments: 'In hot weather, most adults should aim to drink 2.5 to 3 litres of water daily to replenish fluids lost through sweating.' However, she warns not to exceed 1.5 litres per hour, 'as this can dangerously lower your blood salt levels.'
How to hydrate safely
Listen to your body's thirst cues, which Fisher calls 'one of the most reliable ways to maintain internal fluid balance.' Sip fluids gradually and only when thirsty. Adjust intake based on activity and environment: upping intake is more important after an outdoor summer workout compared to a cool day at home. Boost electrolytes mindfully through whole foods like spinach, nuts, bananas, and avocados. Fisher stresses: 'For most people with a balanced diet and moderate activity levels, additional electrolytes are not usually necessary.' In some cases, supplements can cause an imbalance on the opposite end of the scale and should be taken in moderation, such as when exercising for longer than an hour. Seek medical advice if experiencing persistent nausea, headaches, swelling, or confusion.
