Humans, like every other mammals, cannot take oxygen from water. When we dive in water, we have to hold our breath under the surface in order to breathe. Our ability to hold our breath in water is limited. The deeper the dive is, the water pressure increases and compresses the lungs.
Snorkeling
A snorkel is considered to be the simplest breathing equipment when breathing in water. Snorkeler wears a mask that covers the person's eyes and nose and uses a breathing tube in his/her mouth. However, this cannot work below 18 inches from the surface water. That's why, the snorkeler must be close to the surface water when diving.
Diving With An Air Tank
Divers wear special breathing apparatus for long, deep dives. They usually carry tanks that has pressurized air that has the same pressure as the surrounding water. Most divers use scuba tanks for them to breath underwater.
Internal Injury
If the diver takes so much water into his lungs, this could result to flooding the lungs and therefore drowning. Another factor that may result to internal injury is ascending too fast.
Ascending too fast would cause the air inside the body to expand faster than the lungs can. This could lead to traumatic internal injury or even death.
The ability to breathe underwater excites us humans because we cannot breathe underwater. Although it is fun to be able to breathe underwater, we must also take into consideration the necessary precautions to keep us to safety.
References:
https://www.air-n-water.com/breathing-underwater.htm
http://www.elitedivingagency.com/articles/scuba-tank-gas-mixture-divers-use/
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