ELI5: explain how kidneys reabsorp water?

Kidneys reabsorb water by acting like a smart recycling machine that pulls clean water out of your liquid waste and sends it back into your blood so you do not dry out.

Think of your kidneys as your body's cleaning crew. Every day, they clean all your blood by dumping a huge mix of trash and water into tiny cleaning tubes called nephrons. But if your body threw away all that water, you would dehydrate in just a few minutes.

Here is how your kidneys save the water, just like you might save things in everyday life:

• Squeezing out the good stuff: As the liquid travels through the tiny tubes, your kidney uses special minerals, mainly salt, as a magnet. Just like a dry sponge naturally soaks up a spill on the kitchen counter, your salty blood vessels pull the fresh water out of the tubes and back into your body. This natural pulling process is called osmosis.
• Listening to the brain: Your brain constantly checks how thirsty you are. If you are playing outside on a hot day and sweating, your brain sends a chemical message called ADH (Anti-Diuretic Hormone). This message tells the kidneys, "Save every drop of water!" The tubes then open tiny microscopic doors called aquaporins to pull even more water back into your blood.
• Making the final decision: When the kidneys save a lot of water, your pee looks dark yellow because it is mostly just pure waste. But if you drink three big glasses of water, your brain tells the kidneys, "We have plenty of water, let the rest go!" The kidney stops pulling water back, and your pee turns light yellow or clear.