More fluids (within reason) means healthier kidneys, bladder & bowels. Skin too, perhaps, and even possibly your heart.
Again, if you greatly prefered tea or lemonade, that’s all right too, if not taken to extremes.
For the record, you kidneys DON’T work any harder to excrete water, so there really isn’t any downside (aside from the obvious frequent urination) to a healthy person drinking 4-6L of water a day. 10-20L is a differnt story
Here’s a thumbnail sketch of how your kidneys work:
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blood flows through the glomerulus, a sort of “balled-up microfilter” in your kidney. The glomerular filter has a slight negative charge (to help exclude compounds like ling thin proteins), and a pore size corresponding to roughly 500 daltons. Small molecules pass freely, so the initial filtrate has the same concentration of small molecules (like urea or blood sugar) as your blood plasma does.
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the ultrafiltrate is then processed in a long U-shaped tubule (the U- shape is very important, but it’s too complex to explain here.) where various molecules are actively or passively resorbed or excreted. “actively” means “using energy”; “passively” means the tube wall is simply permiable to those compounds, and they diffuse under their own concentration gradiant. The gradients are different in different layers of your kidney.
This causes many interesting quirks. We all have sugar in our urine initially (in he ultrafiltrate), but only diabetics void it, when they have so much urine in their blood that it overwhelms their ability to resorb it. People with gout have to worry about uric acid, which is filtered, then resorbed, then excreted again. Many drugs are used with companion drugs that will modify their excretion (e.g clavulanic acid in the drug mixture “Augmentin” "augments the actual antibiotic amoxicilin by sacrificing itself to active kidney excretion, so the active ingredient is spared). Other drugs like “loop diuretics” can cause undesirable side effects (like interfering with the resorption of potassium, causing excessive potassium loss)
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Water tend to migrate passively when it can to partly balance the different concentrations of various substances.
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the final product of all this this filtration, absorption and excretion (active and passive) goes into tiny collecting tubules which are basically impermeable to everything. At this point, the composition is "locked in"as they flow together into larger tubules and into your bladder. This is why you can’t reclaim water from your dilute morning urine (that is still in your bladder) no matter how desperately you might need it in the afternoon. (A principle that is relevant to a surprising number of threads) You might think it’d be cool if we could resorb that water on demand, but if we could, it’d only cause complex problems. Since the kidney doesn’t actively do anything to water,we’d essentially need an extra kidney-like organ in the bladder to sort everything out. It’s just not worth it
In short strokes: water is too omnipresent in our body to micromanaged – it’d take a HUGE amount of energy-- so instead the body pumps key ions (most famously sodium) across (e.g.) cell or kidney tubule membranes, and the water is allowed to diffuse where it can to try to balance things out.
I agree with the thirsty, check your pee, and also look for other signs, such as fatigue / memory, headaches etc. Using signs in corroboration is likely foolproof.