The short answer is that it all depends on your body weight and activity level. For normal, healthy adults, it is recommended that those aged 18-60 years old consume 35ml/kg of fluid per day (PENG, 2011). For example, if you weight 60kg, you should be drinking 2.1L a day, however if you weigh 50kg you only need to consume 1.75L/day as a baseline. It is important to remember that you should increase your fluid requirements according to your physical activity levels and climate temperature. For example, if you are do an intense gym session, make sure you up your fluid intake prior to, during and after exercise. Additionally, if you are in a hot climate, you will sweat more and lose more bodily fluids, so it is important that you drink more that usual to stay hydrated. If you are dehydrated, have a raised body temperature, or certain medical conditions, you fluid intakes may differ. It is therefore important that a healthcare professional assesses your requirements on an individual basis. A good way to know if you are hydrated is to look at the colour of your urine- it should be a very very pale straw colour is you are well hydrated. If it isn't- drink more! Remember that all fluids count (although watch out for alcohol and caffeine which can dehydrate you). Remember that even fruits and vegetables like cucumber and watermelon are hydrating!