This is an age-old question that has different answers depending on your sex, health, weight and how much exercise or physical activity you undertake.
However, while there is no one size fits all answer, there are certainly some tested and accepted guidelines for water consumption.
The easiest rule to remember and follow is the common “eight glasses of water per day” or at least two litres. As the average adult loses around 2.5 litres of water every day, drinking at least 2 litres of water (the eight glasses) and eating food that will provide you with the other 0.5 litres, will ensure that your lost fluids are replenished.
The Institute of Medicine takes these recommendations one step further and recommends that men consume roughly 3 litres of total beverages a day and women consume 2.2 litres of total beverages a day. While this may seem excessive, it seems to be a suitable figure for active men and women who exercise.
The amount of exercise that you undertake provides the greatest variation in working out how much you should drink. An extra 400-600mls of water is required to compensate for short periods of exercise, but this should be increased for longer periods of exercise. The general rule is for every twenty minutes of sweat-inducing exercise, one glass of water should be drunken.
Pregnancy or breast-feeding also dramatically increases the body’s need for water. It is recommended that pregnant women drink two-four extra glass of fluids daily and women who breast-feed drink an additional three-four glasses of water every day.
Travelling increases the need to drink water, as airplanes have low humidity. You should drink at least one glass of water every hour in the air to help compensate for the high altitude.
One of the biggest mistakes people make when it’s cold is to stop drinking water. In fact, the colder it gets the more water your body needs to maintain its body temperature. Even though one rarely feels like it, you should drink extra water in cold temperatures (or for that matter if in a warm, artificially heated environment).
An extra one or two glasses of water should be consumed prior to spending time in hot weather and if sweating you should drink more than usual.
Any illness will cause your body to lose additional water to the normal amount and therefore constant replenishment is required over and above the recommended daily amount.