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I drink approx 3-4 litres of water a day, so I am not dehydrated, but my urine stays dark yellow all day. I am lead to believe by all the medical articles I have read, that if I am drinking enough fluids, my urine should be dark yellow in the morning, but get lighter throughout the day, and be almost clear by evening. This is not happening. I also read that some medications, vitamins or supplements can cause this, but I am otherwise healthy, and not on any medications, or supplements of any kind. What could be causing this?