ENJOY A WIDE VARIETY OF NuTRITIOuS FOODS
61Guideline 2
2.6 Drink plenty of water
2 .6.1 Setting the scene
Water is essential for life. All biochemical reactions occur in water. It fills the spaces between the cells and
helps form structures of large molecules such as protein and glycogen. Water is also required for digestion,
absorption and transportation, as a solvent for nutrients, for elimination of waste products and to regulate
body temperature.^613
Water is lost from the body in sweating (from 100ml to several 1,000ml/day), insensible losses from the lungs
and skin (approximately 800ml/day), faecal losses (200ml/day) and urine. A minimal urine volume to excrete solute
load is estimated at 500ml/day but may need to be much greater in older people due to declining kidney function.^614
Excluding obvious sweating, the normal turnover of water has been estimated at approximately 4% of total body
weight per day in adults. In a 70 kg adult, this is equivalent to 2,500–3,000ml/day.
Some of this turnover will come from the water contained in foods but the majority of dietary intake comes
from free water and/or other water-containing fluids.8,36 Ambient temperature, physical activity and body size
all influence requirements, creating wide variations in daily needs for water. losses from the lungs and skin
increase at high temperatures, high altitude and low humidity. During summer, when heat stress may be high,
water depletion can lead to heat exhaustion, loss of consciousness and heat stroke.615,616
Details of water requirements for all ages are found in the NRV Document, but for adult males and females
the estimated daily average intake is 2.6 l and 2.1 l (8–10 cups) respectively.^8 This includes all fluids, but it is
preferable that the majority of this intake is from plain water. Water requirements can increase considerably in
high temperatures and in increased physical activity.
There are no reports of any specific hazards from the usual consumption of water by healthy individuals. Excess
water intake can cause hyponatraemia, but this is rare in the general population. In general, self-regulation of
excess water consumption occurs in healthy people in temperate climates.
2.6.2 The evidence for ‘drink plenty of water’
Water is essential for human life because it is required in amounts that exceed the body’s ability to produce it.
Given this, no recent studies investigating the relationship between water consumption and health outcomes
were identified in the literature review. Many commonly consumed fluids provide water, however they may also
be acidic such as low-joule soft drink or contain added sugar, alcohol or caffeine. Recent studies that investigated
intake of these fluids and health outcomes are reviewed below.
Table 2.16: Evidence statements for ‘drink plenty of water’
Evidence statement Grade
Consumption of sugar-sweetened beverages is associated with increased risk of weight gain in adults and children. B
Consumption of coffee of four or more cups per day is associated with reduced risk of type 2 diabetes. B
Consumption of green and black tea is associated with reduced risk of stroke. C
Consumption of coffee is associated with reduced risk of endometrial cancer. C
Consumption of coffee is associated with reduced risk of hepatocellular cancer. C
Consumption of soft drink is associated with increased risk of dental caries in children. C
Consumption of soft drinks is associated with increased risk of reduced bone strength. C
Notes: Grades – A: convincing association, B: probable association, C: suggestive association
Includes evidence statements and gradings from the Evidence Report (literature from years 2002–2009). Does not include evidence from
other sources, such as the 2003 edition of the dietary guidelines (in which individual studies were classified according to their design as
level I, II or III but overall grades for relationships were not derived), although these sources have been used to inform these Guidelines.
Grade C evidence statements showing no association and all Grade D statements can be found in Appendix E.