Imagine yourself being a castaway and literally dying of thirst but surrounded by seawater, like what happens in films. Your mouth is dry and the coolness of the water seems to invite you to drink it. What would you do? You know that it is not safe to drink seawater if there would be other options, but you also know that you could die of thirst or dehydration. What really happens is you drink seawater?
Seventy-one percent of the earth’s surface is water, yet most of it is ocean water that humans cannot consume because of salt. Saltwater is not as deadly as you think it is. Our body depends on salt and water to function. While our bodies use water as universal solvent for macronutrients and help us pump blood, metabolize food, use muscles, our cells also rely on salt in our extracellular fluids for the same actions.
Why Saltwater is Harmful
Consuming a small amount of salt is helpful for our body, but too little or too much can cause damage. The salinity or weight of salt dissolved in 1000 grams of water of human blood is 9 grams. Thus, every thousand grams of fluid has 9 grams of salt and 991 grams of water. Fluids that have the same concentration as the cells or blood in the body are called isotonic. When we take in too much salt, we discharge the excess in our urine to keep our fluids isotonic.
Saltwater is hypertonic or containing more salt than the human blood. It has a salinity of 35. Apparently, consuming extremely hypertonic fluids like seawater confuses our body’s coping mechanism.
What Happens when you Drink Seawater
Diffusion is the transport of matter from high concentration to lower concentration. However, when it comes to saltwater, our cells have biological membranes that keep salt from freely going into the cells. Even if our body can normalize sodium and chloride concentrations up to a certain extent, handling very high concentrations of salt is difficult. It is because the cell membrane is semipermeable. While sodium and chloride may not easily diffuse in and out of our cell, water can. Water corrects the imbalance by moving from the inside to the outside if there is higher salt concentration on the outside of our cells. This is called osmosis. If you are taking in seawater, osmosis can result in a disaster. Since the salinity of seawater is four times of our body fluids, the transfer of water from the inside to the outside will cause the cells to become small, which is not good.
In this situation, the body’s regulatory mechanism is potentially lethal. The change in sodium concentration outside the cell is to be blamed. To regain isotonic state for cell survival, the body will eliminate excess sodium from the extracellular fluids and secrete urine. However, our kidneys can only produce urine that is a bit saltier than saltwater. Thus, to remove excessive amount of sodium, we urinate more than what we dank, leading to dehydration. That means if your consuming seawater, you are not taking in any water but are bringing a net loss that leads to reduced body fluid, dry mouth, muscle cramps and thirst.
When fluid is lost, our body will try to compensate by increasing heart rate and inhibiting blood vessels to keep blood pressure and flow to organs. You are more likely to feel nauseous, weak or even delirium. The more you become more dehydrated, the body’s coping mechanism could already fail. If you still don’t take any water to counter the effects of excessive sodium, the other organs and the brain will receive less blood that leads to coma and eventually death.
Drinking small amount of seawater will not kill you. The message is that salt and water should be consumed separately. Any salt intake should be accompanied by ample amount of freshwater. Humans are not like sea creatures that deal with salinity by acting as osmotic conformers and regulators. While we are not able to do that, we can only use available technology to make surface water potable, such as buying a system from one of the top water softener brands to remove metal cations from hard water, making it more compatible with soap or our plumbing. As for seawater to be drinkable, it is much harder than you think.