Guide · Water

Why you must never drink seawater or urine

When you're desperately thirsty, seawater and urine can seem like an option. They're not. Both make dehydration worse and can speed up a dangerous decline.

Why seawater is dangerous

Seawater is roughly three times saltier than your blood. Your kidneys can only get rid of salt by flushing it out in urine, and they can't make urine as salty as seawater. To clear the salt from a mouthful of seawater, your body has to use more water than you drank.

So every drink of seawater leaves you more dehydrated than before. It also causes vomiting and diarrhoea, which lose even more fluid. In time it can cause confusion, seizures and kidney failure.

Mixing seawater with fresh water doesn't make it safe — it just wastes your fresh water.

Why urine is dangerous

Urine is your body's way of getting rid of waste and excess salt. When you're dehydrated, your urine is darker and more concentrated. Drinking it puts those waste products straight back in, and your kidneys then need even more water to flush them out again. It may feel like it helps for a moment, but it works against you.

The same goes for other body fluids, alcohol, and fluids from car radiators or engines, which can be poisonous.

What to do instead

1. Reduce water loss. Stay in the shade, rest, keep covered, breathe through your nose and avoid work in the heat.
2. Collect rain. Spread out any sheet, tarp or clothing to catch rain, and store every drop.
3. Collect dew with cloth in the early morning.
4. Make a solar still. Dig a hole, put a container in the middle, cover with clear plastic sealed at the edges, and place a small stone in the centre above the container. Condensation drips into the container. You can put seawater or urine in the hole around the container — the still evaporates the water and leaves the salt and waste behind. Output is slow, often well under a litre a day, so don't overwork to build one.
5. At sea, many life rafts carry a desalting kit or hand pump. Use them if you have them.
6. Eat less if you have little water, especially salty or high-protein food.

If someone has already drunk seawater or urine

Stop them drinking more. Give fresh water in small, frequent sips if you have any. Watch for vomiting, confusion or drowsiness, and get medical help as soon as you can by calling your local emergency number (112 in Europe and many other countries, 911 in North America).

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