Why is seawater undrinkable?

When viewing Earth from space, a predominant color emerges, which is why our planet is often referred to as the Blue Planet. Approximately three-quarters of our world's surface is enveloped by water. However, there's a crucial caveat: 96.5 percent of this water is contained within the oceans. If you recall your first visit to the seaside with your parents, you probably learned that drinking ocean water is a big no-no. So, why is ocean water saline and unfit for consumption? There are two primary reasons.

Firstly, runoff water from the land, including rainwater, plays a role. Rainwater is slightly acidic, with a pH ranging between five and five and a half. For comparison, pure water has a pH of seven, while battery acid measures a bit over zero on the pH scale. When rainwater falls on the ground, it erodes rocks, releasing ions like sodium and chloride. These ions eventually find their way into rivers and streams that ultimately flow into the ocean. While some of these ions are removed by living organisms, the majority remain, leading to an increase in their concentration over time. This contributes to the salinity of ocean water.

Another significant factor is the hydrothermal vents located on the ocean floor. These vents release a hydrothermal fluid, which may sound complex but is easily understood. Water seeps into gaps on the ocean floor, where it is heated by magma from the Earth's core. This process triggers a chemical reaction that eliminates oxygen from seawater while adding metals like iron and zinc. During underwater volcanic eruptions, these vents discharge the metallic water back into the ocean. Over time, salt and other minerals accumulate on the sea floor, forming domes. Similar deposits can be found beneath dry land, and some regions, like the Gulf of Mexico, have numerous salt domes beneath the waves. These domes influence the salinity of the surrounding water.

Various factors determine the salinity of a body of water, including evaporation, air temperature, and precipitation. Generally, salinity is lower near the equator and the poles, while the oceans and seas between these regions tend to have higher salinity levels. Scientists estimate that dissolved salts account for approximately three and a half percent of the weight of the world's seawater. In contrast, waters that flow into the ocean, such as those from lakes and rivers, are fresh water.

To understand why seawater is salty, we must delve into Earth's history. Researchers believe that ancient seas were not as saline as they are today. Over time, rainfall washed away minerals from the Earth's surface, transporting vast amounts of salt into the oceans. This process has been ongoing for more than 3.8 billion years, with approximately 4 billion tons of dissolved salts entering Earth's oceans annually. The input and output of salt are relatively balanced, maintaining the stability of seawater's salinity.

But why can't we drink seawater? The answer lies in its salt content. The percentage of salt in seawater is nearly four times higher than that in our blood. Our bodies cannot process such a high concentration of salt. When we consume salt through food and drinks, it is known as dietary salt. The World Health Organization recommends a daily intake of no more than a teaspoon per person to maintain heart health. Centuries ago, seafarers relied on salted meat for preservation, as refrigeration was unavailable. Salted beef and pork were staple foods at sea, as fresh fruits and vegetables spoiled quickly.

The issue with drinking seawater is its high salt content. Our bodies absorb both water and salt when we consume it. This combination ends up in our bloodstream, and the kidneys are responsible for removing excess salt. However, the kidneys require water to carry out this function efficiently. The higher the salt content, the more water the kidneys need to eliminate the salt. Repeatedly consuming seawater leads to dehydration, as you lose more water than you gain. Submarine mammals like whales and seals, as well as seagulls, can drink seawater because their kidneys are highly efficient. Birds have special glands in their beaks that prevent salt from entering their bloodstream. Surprisingly, the camel is the only land animal capable of drinking seawater. Fish also drink seawater, with their gills and kidneys assisting in expelling excess salt.

For humans to consume seawater, it must undergo desalinization, the process of removing salt. However, the vast quantities of salt make this process challenging. If all the salt from Earth's oceans were removed, we'd have an endless supply of drinking water, but this comes at a significant cost. Numerous plant and animal species are adapted to saltwater environments, including plankton, the foundation of marine life. Switching to freshwater would disrupt their ecosystems.

Additionally, freshwater is less dense than saltwater, causing the Arctic ice cap to sink, potentially triggering massive tidal waves. While global-scale desalinization may seem appealing, it poses various challenges, primarily due to its substantial energy requirements and environmental impact. Less than half a percent of the world's drinking water comes from seawater desalinization, and the demand for freshwater continues to grow. The energy-intensive nature of desalinization necessitates dedicated power stations, making it a costly endeavor.

In conclusion, while the concept of drinking seawater has been explored throughout history, it remains impractical on a global scale. The challenges of desalinization, the disruption to ecosystems, and the energy requirements make it a complex and costly solution. Therefore, the idea should be taken with caution, just like adding a grain of salt to any grand plan.