Drowning in Freshwater versus Saltwater  

Why More People Drown in Freshwater

Drowning in freshwater is different from drowning in saltwater. In fact, more people drown in freshwater than saltwater. Around 90% of drownings occur in fresh water, such as swimming pools, bath tubs and rivers. This is partly because of the chemistry of the water and how it relates to osmosis. Here's how it works.

It's much harder to survive drowning in freshwater because osmosis of fresh water into cells damages them.

Drowning in Saltwater

Drowning involves suffocating while in water. You don't even need to breathe in the water for this occur, but if you do inhale salt water, the high salt concentration prevents the water from crossing into lung tissue.
If you drown in salt water, it's usually because you can't get oxygen or expel carbon dioxide. Breathing in salt water acts as a physical barrier between the air and your lungs. If the salt water is removed, you can breathe again.

However, that does not mean there won't be lingering effects! Salt water is hypertonic to the ion concentration in lung cells, so water from your bloodstream enters your lungs to compensate for the concentration difference.

Your blood thickens, putting strain on your circulatory system. The stress on your heart can lead to cardiac arrest within 8 to 10 minutes. The good news is, it's relatively easy to rehydrate your blood by drinking water, so if you survive the initial experience, you are well on the road to recovery.

Drowning in Fresh Water

You can die from breathing fresh water even hours after you avoided drowning in it! This is because fresh water is more "dilute" with respect to ions than the fluid inside your lung cells. Fresh water doesn't cross into your skin cells because keratin essentially waterproofs them, but water rushes into unprotected lung cells to try to equalize the concentration gradient across the cell membranes. This can cause massive tissue damage, so even if the water is removed from your lungs, there is a chance you might not recover.

Here's what happens: Fresh water is hypotonic compared with lung tissue. When water enters cells, it swells them. Some of the lung cells may burst. Because capillaries in your lungs are exposed to the fresh water, water enters the bloodstream. This dilutes your blood. Blood cells burst (hemolysis). Elevated plasma K+ (potassium ions) and depressed Na+ (sodium ion) levels may disrupt the heart's electrical activity heart, causing ventricular fibrillation. Cardiac arrest from the ion imbalance may occur in as little as 2 to 3 minutes.

Even if you survive the first few minutes, acute renal failure may occur from concentration of hemoglobin from the burst blood cells in your kidneys. If you drown in cold fresh water, the temperature change as the cold fresh water enters your bloodstream may even cool your heart enough to cause cardiac arrest from hypothermia. On the other hand, in salt water, the cold water does not enter your bloodstream, so the effects of temperature are mainly limited to heat loss across your skin.