how much fluid do I need to stay hydrated?

Water is a vital nutrient necessary for the health and integrity of every cell in the body. There are many ways we lose water on a daily basis. For example, we lose water from our lungs as we breath, from our skin through sweating and from urine. As our bodies cannot store water, we need to take in fresh supplies every day to replenish any losses. There are many factors involved in calculating how much fluid you need on a daily basis, such as your body size and composition, diet, activity level and the weather conditions. For example, sedentary people or those living in colder climates may need to drink less fluid than those living in warmer climates and who exercise frequently. Ideally, the majority of fluid intake should be from plain water where possible.1 As a guide, the following fluid intakes are recommended:1
Age Group Fluid Intake
Infants 0–6 months 700ml (from breastmilk or formula)
Infants 7–12 months 900ml (from breastmilk, formula and other foods and drinks)
Children 1–3 years 1 litre (about 4 cups)
Children 4–8 years 1.2 litres (about 5 cups)
Girls 9–13 years 1.4 litres (about 5‐6 cups)
Boys 9–13 years 1.6 litres (about 6 cups)
Girls 14–18 years 1.6 litres (about 6 cups)
Boys 14–18 years 1.9 litres (about 7‐8 cups)
Women 2.1 litres (about 8 cups)
Men 2.6 litres (about 10 cups)
Pregnant and breastfeeding women have increased fluid requirements. Water is needed to form amniotic fluid surrounding the baby, support the increased blood volume and to produce breast milk. Pregnant women should drink an extra 300ml of fluids per day and breastfeeding women, an extra 700ml.2 While water is an important part of maintaining a healthy body, very occasionally people can drink too much e.g. participants of endurance sports. Doing so can dilute your blood and lead to low sodium levels. When this happens, the water level in your body rises and your cells begin to swell. This swelling may cause health problems, ranging from mild to severe.3