STAYING hydrated seems a simple enough concept.

Drink three or so litres of water per day and the body should have enough fluid in the system to complete all of the processes for healthy living, in an optimal biological environment.

But there are other factors which influence how much fluid and what type should be taken on.

Temperature is one important factor, and the demands placed on the body is another. While water is usually all that’s needed, when it’s extremely hot, or long or intense bursts of physical activity are taking place, it may benefit to rethink what we use to quench our thirst.

The main reason is that during these conditions the body loses more than just water as it battles to maintain a normal body temperature of 37 degrees.

Sweating is the body’s way of cooling down and dispersing heat, but sweat is made up of more than just H20.

Electrolytes are minerals in the blood and other bodily fluids that affect the amount of water in our bodies, the acidity of our blood and how our muscles function.

We lose electrolytes when we sweat, and if we sweat too much without replacing the lost fluid and electrolytes we can become dehydrated.

Dehydration can impair exercise, affect mental focus and cause health problems.

Sports drinks are designed to simultaneously replace fluids and electrolytes, and provide fast-digesting carbohydrates to replenish energy stores. There are three main types.

Hypotonic drinks contain 2-4g carbohydrates per 100ml and a small amount of the electrolyte sodium. These suit those needing fluid without excessive carbohydrate intake.

Isotonic sports drinks are usually made up of 6-8g of carbohydrates and 50-60mg of sodium per 100ml. These tick most boxes for most athletes performing for over 60 minutes duration.

Hypertonic drinks contain even more carbohydrates and gear towards refuelling post-exercise or in conjunction with other hydrating drinks during very long or intense activity.

Low-intensity activities such as walking, and moderate exercise lasting under an hour, usually require only water. Replace sweat lost in more demanding or longer sessions with an isotonic drink and take on 500ml of water an hour before any exercise session.

As a general rule, pale yellow or straw-coloured urine indicates good hydration. Dark yellow, or orange, shows you are in need of a good drink.

Ronny Terry is a Swindon-based personal trainer and fitness writer. Sign up for FREE weight loss and fitness tips at www.switchfit.co.uk.