How long should a gallon of water last you? A comprehensive guide
                                
                                
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                                    4 min read                                
                            
                                The human body is composed of about 60% water, yet many people are chronically dehydrated. Knowing exactly how long should a gallon of water last you is a critical piece of information for both optimal daily health and emergency preparedness, where a gallon-per-person-per-day rule is common.