The central hypothesis is that improving hydration through increased water consumption will change the relative abundance of mucolytic bacteria found in the stool. Therefore the specific aims are 1) to quantify intervention effects on fecal microbiota relative abundance and plasma lipopolysaccharide binding protein, 2) observe the effects of the intervention on bowel frequency and signs/symptoms of gastrointestinal stress, and 3) to investigate relations between executive function and hydration status.

A single arm 3-week hydration intervention will be employed where participants increase their water consumption to 2 (F) or 2.5(M) liters per day which is approximately 70% of the AI for daily water consumption. Pre-test and follow-up measures of fecal microbiota, urinary hydration status, cognitive function, circulating markers, and dietary intake will be assessed at baseline and at 3-week follow up via laboratory visits.

Inclusion Criteria:

• 19-50 years of age
• 18.5-34.49 kg/m2
• 24-hour UOsm above 500 mOsm/kg
• No antibiotic use over the past 3 months
• Absence of metabolic diseases and use of diuretics
• Agree to maintain typical diet intake (e.g., dietary fiber) patterns during intervention
• Avoid consuming prebiotic and probiotic supplements during study participation
• Not pregnant
• Agree to follow the study protocol

Exclusion Criteria:

• <19 or >50 years of age
• <18.5 or >34.49 kg/m2
• 24-hour UOsm <500 mOsm/kg
• Antibiotic use over the past 3 months
• Metabolic diseases and use of diuretics
• Not agree to maintain typical diet intake (e.g., dietary fiber) patterns for the duration of the
• intervention
• Not agree with avoiding consuming prebiotic and probiotic supplements during study participation
• Pregnant
• Not agree to follow study protocol