Why does less water intake lead to dark yellow urine, while drinking more water makes it normal?

Yellow urine when drinking little water, and normal urine color when drinking more, may be a physiological phenomenon or related to pathological factors such as urethritis or pyelonephritis. The specific analysis is as follows:

I. Physiological Phenomenon

When daily water intake is low, urine output decreases and the urine becomes concentrated, leading to darker urine color. However, this typically does not cause other symptoms such as frequent urination or painful urination. When fluid intake increases, urine volume rises, concentration decreases, and urine color returns to normal—sometimes even becoming colorless. This is considered a normal physiological phenomenon that generally requires no special intervention. It is recommended to adjust daily water intake according to weather, physical activity, and individual needs.

II. Pathological Factors

1. Urethritis
This is mainly caused by infection of the urethra with gonococcal or non-gonococcal pathogens. After urinary tract infection, the reabsorption and filtration rate of urine may decrease, resulting in changes in urine color. Treatment may include medications such as levofloxacin hydrochloride capsules or ciprofloxacin hydrochloride capsules, taken under medical supervision.

2. Pyelonephritis
This condition is primarily caused by pathogenic microorganisms inducing inflammation in the renal pelvis and kidney tissue. If left untreated, severe cases can impair kidney function, reduce urine output, and lead to concentrated urine. Treatment may include antibiotics such as cefixime granules or amoxicillin capsules, taken as directed by a physician.

In addition to the above causes, yellow urine may also result from kidney stones, renal failure, or kidney cancer. Individuals experiencing persistent symptoms should seek medical evaluation and receive targeted treatment from a healthcare provider.