From the Guidelines
The largest percentage of water taken in daily is used by the body for cellular metabolism, temperature maintenance, and elimination of wastes, with the kidneys playing a crucial role in regulating water levels and removing waste products through urine production. According to the study published in Advances in Nutrition 1, water is necessary for normal cellular metabolism as well as elimination of wastes through urination, perspiration, and bowel movements and has a role in temperature maintenance and lubrication of joints. The study also notes that approximately 74% of the US population receives water with sufficient fluoride for the prevention of dental caries.
The daily total water requirements increase with age, and general daily recommendations for healthy women and men are ∼2.7 L and ∼3.7 L of total water, respectively, including fluids from water, other beverages, and food 1. Another study published in Clinical Nutrition 1 recommends an Adequate Intake (AI) of 2.0 L/day for women and 2.5 L/day for men of all ages, with 80% of these fluid needs coming from drinks.
Key points to consider include:
- The kidneys filter approximately 180 liters of fluid from the bloodstream every day, though most of this is reabsorbed, with only about 1-2 liters ultimately excreted as urine.
- Water is vital for other bodily functions including digestion, circulation, temperature regulation, and cellular processes.
- Maintaining adequate hydration is crucial for optimal kidney function, with most adults needing about 2-3 liters of total water intake daily, though individual needs vary based on factors like activity level, climate, and overall health 1.
- Individual fluid needs are related to energy consumption, water losses, and kidney function, so larger people may require more fluid, and needs may also be higher in extreme temperatures or at times of greater physical activity 1.
From the Research
Water Functions in the Body
The human body uses water for various essential functions, including:
- Acting as a building material
- Serving as a solvent, reaction medium, and reactant
- Carrying nutrients and waste products
- Regulating temperature
- Acting as a lubricant and shock absorber 2
Daily Water Requirement
The daily water requirement is not based on a minimal intake, but rather on experimentally derived intake levels that meet the nutritional adequacy of a healthy population 2.
- A sedentary adult should drink approximately 1.5 liters of water per day 2
- Total water intake (TWI) should be at least 1.8 L/24h to maintain water balance and prevent mild neuroendocrine defense of body water 3
Water Balance Regulation
The regulation of water balance is essential for maintaining health and life, and is controlled by the central nervous system and several organ systems 3.
- Minute changes in plasma osmolarity trigger homeostatic mechanisms to regulate water balance 2
- Healthy adults regulate water balance with precision, but young infants and elderly people are at greater risk of dehydration 2
Importance of Water Intake
Water intake is critical for human health, and its importance has received more attention recently due to the shift towards consumption of large proportions of fluids as caloric beverages 4.