I am 6'4'' and weigh about 225 lbs. How can I figure out the optimal amount of water to drink daily? Thank you.

By symptoms. Given normal metabolism and no major medical problems, you should drink water so that you're urinating regularly (clear yellow urine, not colorless, and not dark). You shouldn't be thirsty. If you take supplements, have certain medical problems, or using illicit drugs, you could certainly be damaging your kidneys (but more water won't help). See your primary care doctor, and/or nephrologist.