Water retention (oedema) occurs when excess fluid accumulates in body tissues, causing swelling, puffiness, and temporary weight gain of 1–3 kg in mild cases. The 6 most common causes are high sodium intake, hormonal fluctuations, prolonged sitting or standing, certain medications, heat exposure, and underlying medical conditions including heart failure and kidney disease. This guide covers why the body retains water, how to distinguish normal retention from medical oedema, and evidence-based strategies for reduction.
What Causes Water Retention
The body maintains fluid balance through a feedback loop between the kidneys, hormones, and the cardiovascular system. Water retention occurs when this loop is disrupted, causing the body to hold more fluid in tissues than normal.
Sodium intake is the most common dietary cause. Sodium attracts water — high-salt meals cause the body to retain extra fluid to maintain sodium concentration balance. A single high-sodium meal can cause 0.5–1 kg of temporary water weight gain within 24 hours. This resolves naturally as the kidneys excrete the excess sodium and associated water over 1–2 days.
Hormonal changes cause cyclical water retention in women. Oestrogen and progesterone fluctuations during the menstrual cycle, pregnancy, and menopause alter kidney sodium handling, producing fluid retention of 1–3 kg that peaks in the 5–7 days before menstruation and resolves within 2–3 days of the period starting.
Inactivity reduces the return of fluid from tissues to the bloodstream. Prolonged sitting (desk work, long flights) causes fluid to pool in the lower legs and feet due to gravity. Walking, calf raises, and leg elevation reverse this mechanical pooling.
Medications including corticosteroids, non-steroidal anti-inflammatory drugs (NSAIDs), blood pressure medications, and some antidepressants can cause fluid retention as a side effect. Medication-related oedema should be discussed with a prescribing doctor rather than self-managed.
Medical conditions — heart failure, kidney disease, liver disease, and venous insufficiency — cause chronic water retention that requires clinical management. Persistent swelling that does not resolve with dietary and lifestyle changes, or that affects one leg significantly more than the other, warrants medical assessment.
How to Reduce Water Retention
Reducing water retention focuses on supporting the body's natural fluid-balance mechanisms rather than restricting fluid intake. Counterintuitively, drinking more water reduces retention — adequate hydration signals the kidneys that fluid is abundant and excess can be safely excreted.
Reduce sodium intake to below 6g per day (the UK recommended maximum). The largest sodium sources in the typical UK diet are processed foods, bread, cheese, and restaurant meals. Cooking from fresh ingredients and seasoning with herbs rather than salt reduces sodium load significantly.
Increase potassium intake through bananas, sweet potatoes, spinach, and avocados. Potassium counterbalances sodium's water-retaining effect by promoting sodium excretion through the kidneys.
Move regularly — even 5 minutes of walking per hour reduces gravity-dependent fluid pooling. Calf muscle contraction acts as a pump, returning venous blood and lymphatic fluid from the lower legs to central circulation.
Elevate the legs for 15–20 minutes when swelling is noticeable. This uses gravity to assist fluid return from the ankles and feet.
The constraint is that diuretics (water pills) are sometimes used to treat water retention but should only be taken under medical supervision. Over-the-counter herbal diuretics (dandelion tea, parsley extract) have mild effects and are generally safe but are not appropriate for retention caused by medical conditions.
Water Retention vs Dehydration
Water retention and dehydration are not opposites — they can coexist. A person can be dehydrated (insufficient fluid for organ function) while simultaneously retaining water in tissues. This occurs because dehydration triggers the kidneys to conserve sodium, which in turn causes tissue fluid retention.
This paradox is why restricting water intake to "reduce bloating" is counterproductive. Drinking less water worsens both conditions — the body retains more aggressively when it perceives fluid scarcity, while organ function suffers from the reduced supply.
The evidence-supported approach is consistent, moderate water intake — 2–2.5 litres per day for most adults — combined with sodium reduction and regular movement. This supports the kidneys in maintaining proper fluid balance without triggering conservation responses.