How do you say im thirsty in Spanish?

Tengo sed, which means I have thirst is more common. Yo soy sediento literally means I am or I'm thirsty. To apply that to other subjects, you need to conjugate tener to the subject. So tener sed means 'to have thirst', so if you want to say "you are thirsty" you would conjugate 'tengo' into 'tienes', so you would say "Tu tienes sed."