Fun fact: caffeine's actual toxicity is so low that if you were to off yourself by drinking coffee, water overdose would get you before caffeine overdose.
@jmw150 this might apply to cold brew, if you can achieve a high enough concentration
@Amikke Caffeine intoxication is 1 part euphoria with 2 parts explosive diarrhea/projectile vomiting and panic attacks. I consume around a gram a day. Don't worry, I'm a Mathematician and no stranger to stimulants. ;) 
@AmpBenzScientist water's fine, I've heard of an experiment where an intern accidentally measured an order of magnitude more caffeine than intended into plain glasses of water and sent 2 people to the hospital for weeks. It's just that the concentration of caffeine in water to achieve its intended effect is much lower than what's needed to be toxic.