If you are after an exact number- 30-40ml/kg of body weight is a pretty good guideline. Without the need to measure anything though, a good indicator can be the colour of your urine:
closer to clear = well hydrated,
loser to yellow = not so hydrated.
Adequate hydration is super important for every cell, tissue, and organ to function properly. We know water is incredibly important in:
- regulating body temperature (which is super important in warmer temperatures and when exercising)
- keeping joints well lubricated
- preventing infections
- delivering nutrients to cells
- keeping all organs functioning properly

Consider the fact that one of our main ways of regulating body temperature is through sweating. So, when we are sweating more, we require more fluid. Inadequate intake of fluids can lead to dehydration.
Negative effects of dehydration include:
- Headache
- Sleepiness
- Lack of concentration
- Low energy
- Dry mouth
- Impaired exercise performance
- Constipation
What drinks contribute to hydration?
Any fluids, including soup and coffee contribute to your hydration target. Drinks that are not recommended include sugary drinks (such as soft drink, fruit juice) and alcoholic drinks (which act as diuretics too). The negative effects of sugar and alcohol outweigh the benefits of the hydration these offer. Remember that drinks high in fat or sugar provide added calories to the diet that may not be desirable for those watching their weight. Choose naturally sugar-free drinks to provide your fluid needs wherever possible.