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Choose a spot in the water to sink. Take a vertical position in the water with your feet pointing down. Take some slow, deep breaths to fill your lungs with oxygen. Get into a tucked position. Sink. Return to the surface.
You can completely submerge yourself in any body of water that is higher than you are tall, or that will cover your head when sitting (or even lying down, such as in a wading pool). The most important factor to consider for picking a spot is to observe your surroundings. Always approach holding your breath underwater with caution, especially in a crowded public pool where people are engaged in many different activities and not paying attention to others. If you want to sink to the bottom of a pool, you may think choosing a spot near the wall is safest. But, remember that people will be entering the water around all edges of a pool. It may be better to find a relatively isolated place, away from where people may be entering the water and away from large groups. Also, keep your distance from the pool drain, which can exert hundreds of pounds of suction and can cause injury and death.Have a friend keep an eye out for you while you're below the surface. If you're swimming underwater, keep an eye out for traffic and remember that other swimmers will not necessarily be looking out for you. Ideally you can chart a clear path ahead of you to the other side, one that will stay clear until you get there. If you're in the shallow side of the pool, you will likely be standing. If you're in a part of the pool where the water is higher than you are tall, your body will assume a vertical position with ease as, generally, your lower body will be heavier than your upper body. Do not hyperventilate. Taking several fast breaths in a row before submerging yourself is known as DUBB, "dangerous underwater breath-holding behaviors" and can cause hypoxic blackout, which can lead to brain damage, fainting, and death. Pull your knees in and hold them close to your chest by wrapping your arms around them. This tucked position changes the amount of space you're taking up in the water and will allow you to fall deeper into the water and to more easily remain underwater. Objects, and bodies, sink in water if they have a higher density than the body of water. An object's density depends on its mass and volume--the amount of space it takes up. As such, taking up less space in the water will help you sink. Release air bubbles slowly through your nose. You can let them out of your mouth as well and they can be bigger, but you'll sink faster. You may also do both and let out small bits of air, puffing your cheeks between blowing air out. Let your head and body sink into the water. When your feet hit the bottom of the pool, sit in a comfortable position, such as cross-legged or holding on to your knees in front of you. When you're ready or running out of breath, look up to make sure nothing and no one is in your way to the pool's surface. Whether seated or standing, press firmly into your feet and stretch your arms skyward to shoot or swim upwards.