Why doesn't being surrounded by gallons of water in a swimming pool cause sodium imbalances and/or water intoxication? The pool water is isotonic with your internal body fluids.

It is impossible to sweat in a swimming pool; therefore, your body loses no sodium.

Your skin is not as permeable as the lining of your digestive system.

The chlorine in the pool water prevents your body from losing sodium to the surrounding environment, or Swimming in pool water can cause a sodium imbalance; this is why swimming in the ocean is preferable.

The correct answer is: Your skin is not as permeable as the lining of your digestive system.

Explanation:

Pool water is mostly composed of water with some chlorine in it. This is why it could never be true that pool water is isotonic with a person's internal fluids, where half of the osmotic pressure is given by sodium. For pool water to be isotonic with our internal body fluids, it should be a 0.9% NaCl solution.

The chloride in the pool water has no special properties that make your body not lose electrolytes.

The reason why swimming in a pool doesn't cause sodium imbalances is because the skin is not as permeable as the lining in our digestive system. We don't absorb water or ions through our skin. The only way we can get more water and electrolytes in our bodies is by ingesting them when drinking water or eating food. Then, our digestive system absorbs it, and after that, the kidneys dispose of the excess water or electrolytes.