Most people think of urine as the result of drinking too much water or juice. But what many don’t realise is that urine is actually made from your blood, not directly from what you drink.
As Dr Shyam Varma, Consultant, Urologist and Renal Transplant Surgeon, Kokilaben Dhirubhai Ambani Hospital, explains, “Yes, urine is formed from the blood, not directly from the liquids you drink. While the fluids you consume do contribute to hydration, it is your blood plasma, the fluid portion of blood, that is continuously filtered by the kidneys to form urine.”
This process happens inside your kidneys and is part of a carefully balanced system that keeps your body healthy by removing waste and excess substances. Let’s break it down.
through a detailed three-step mechanism inside the kidneys: filtration, reabsorption, and secretion. These processes take place inside microscopic structures called nephrons, of which each kidney has over a million.
“Blood enters the kidneys through the renal arteries, which branch into smaller vessels ending in a cluster of capillaries called the glomerulus,” explains Dr Varma. “This is located inside a structure known as Bowman’s capsule.”
Think of this stage as the body’s natural sieve. The glomerulus filters out water, glucose, amino acids, salts, urea (a waste product), and other small molecules from the bloodstream. However, large molecules like proteins and blood cells are too big to pass through and stay in the blood.
Next, the filtered fluid moves through the renal tubules, including the Loop of Henle. “During this stage, around 99% of the filtered water, essential nutrients, and electrolytes are reabsorbed back into the blood via surrounding capillaries,” says Dr Varma.
This step ensures the body retains what it needs—like glucose and sodium—while getting rid of waste. It’s also how your kidneys maintain fluid balance and blood pressure.
This final step fine-tunes your body’s internal chemistry. Dr Varma explains, “Additional waste substances like potassium, hydrogen ions, and certain drugs are secreted from the blood into the tubules to be excreted. This step is crucial for maintaining the body’s acid-base and electrolyte balance.”
The leftover fluid, now called urine, consists of water, urea, creatinine, salts, and other metabolic waste products. It collects in the renal pelvis, travels through the ureters to the bladder, and exits the body via the urethra.
Dr Varma summarises, “Urine is a by-product of blood purification. Its formation is essential for removing toxins, maintaining pH, blood pressure, and ensuring homeostasis.”
So while hydration certainly matters, what you’re really doing when you urinate is clearing your blood of waste. Your kidneys never stop, they’re filtering your blood around the clock.
