How many cups of water for yellow urine to turn clear? is it 8 cups?

Unknown: There is no definitive amount of water that would result in this color change, It will depend more on your size and your fluid defecit.

Varies: Urine is always a shade f yellow, though darker shade often does indicate need to drink more fluids (preferably without caffeine, which acts as a diuretic) . The amount needed depends on size & weight f person, activity level, diseases person may have (diabetes, heart disease, etc) & medications they take, but 3 r more extra 8 oz glasses of fluid daily is a reasonable start in many cases