We hear a lot about what we should eat to stay healthy, but there's one thing we need even more than food each day – and that's water. Although we all know the importance of drinking enough water during the hot summer months, many people don't realise they need to drink plenty of water all year round. Every part of your body needs water to work properly, but water is particularly important for keeping the kidneys healthy. Dehydration (lack of water) is one of the reasons why people develop kidney stones.

I don't need water because I don't get thirsty, some people say. But that's because thirst can be slow to develop – often we don't feel thirst even when our bodies need fluid. We often confuse thirst with hunger too. Sometimes when you think your body is asking for food, what it really needs is water. This is why it's a good habit to drink water regularly – whether you feel thirsty or not.

But I don't need water because I drink a lot of coffee and tea is another common remark. Tea and coffee are okay in moderation, but larger amounts aren't good substitutes for water – both these drinks contain caffeine, which make your body lose fluid.

Other questions people ask about water are:

How much water should I drink each day? Most of us need between 1.5 and 2.5 litres each day. But if the weather is hot or you are exercising, you need more.

Won't drinking water before exercise cause cramps? No. This is an old fashioned idea. You need water both before and after exercise. Unless you are doing vigorous exercise for long periods, there's no need to drink special sports drinks – water is good enough.

But I drink lost of juice why do I need water? Although it's okay to have a glass of fruit juice each day, it's better to drink more water. But if you really like the taste of juice, try drinking half juice and half water. Besides being more expensive, too much fruit juice can contribute to weight problems and tooth decay. This is why it's good to get children into the habit of drinking water – not just juice – right from the start. If you give a child a "comfort" bottle at night, make sure it contains nothing but plain water – giving juice, milk or any drink with added sugar at night is a common cause of tooth decay.

If I drink a lot of water, won't I retain fluid? No. Many women retain fluid before a period and think that drinking less water will help. But in fact they need to drink more. One of the causes of fluid retention is having too much of a mineral called sodium in the body. But drinking water helps get rid of sodium.

Doesn't drinking water make you go to the toilet at night? This shouldn't be a problem if you have plenty of water during the day, and drink only a little fluid at night. If frequent urination is making you restrict your fluid intake, talk to your doctor- there may be a problem which needs treatment. Frequent urination (along with "leaking") is common, especially in women who have had children. But this can usually be helped by simple exercises to strengthen the bladder – your doctor can refer you to someone who can help. Drinking enough fluid is important for good health and it's better to find a solution for frequent urination rather than drink too little.

With the heat wave we experiencing these last couple of days, we really need to drink a lot of water in order to rehydrate ourselves.