DEAR MAYO CLINIC: I know I need to stay hydrated while I exercise but what is the best fluid? I’m wondering how much I should drink and if I need to drink special water as someone mentioned alkaline water. Is alkaline water better at rehydrating your body than nonalkaline, or plain, water?

ANSWER: Staying hydrated during exercise is important. You can become dehydrated if you take in too little. But you can actually cause problems, such as exercise-induced low sodium or hyponatremia, if you take in too much fluid.

The purpose of rehydrating — whether with water or electrolyte-containing beverages — is to pull fluid back into our system so our organs can function properly.

How much to drink and when is dependent on each individual. The general rule of thumb at this point among physicians is to drink to thirst. Although there are guidelines for hydration before, during, and after exercise, look and listen to your body as the best indicator when you need hydration.

Certainly during summer months, when the weather is hotter and you may be exercising outdoors, you may want to take in more fluid than usual.

For most people, plain water is best. Depending upon how extensively you exercise, you can consume about half your fluid intake in water and half in a beverage that contains electrolytes and some carbohydrates. The reason you want a beverage that includes both is that when you sweat, your body is losing fluid, along with those electrolytes, such as sodium and chloride. Carbohydrates provide fuel for your working muscles. Be mindful of the amount of sugar, though.

Many people don’t drink enough water, and they may feel better after increasing hydration, no matter the source.  So, it’s probably not the alkaline nature of the water that’s of benefit. It’s the water. Certainly it is your choice if you want to add alkaline water to your fluids but it’s important to understand the definition of alkaline water and how your body works.

Scientists use pH to describe how acidic or basic a substance is, with a range from 0 to 14. Pure water has a pH of 7, meaning it’s neutral. Fluids with a pH under 7, such as coffee and soda, are acidic. Substances with a pH over 7, such as baking soda, are basic, or alkaline.

Alkaline waters have a pH around 8 or 9. Some vendors use water that has a naturally higher pH, while others say that they create alkaline water through an ionization process. Regardless of what you eat or drink, your body is good at regulating your blood pH through organs such as your lungs and kidneys.

There are many claims out there about alkaline water, including that it can rehydrate the body better, it will detoxify and “balance” your body, help you lose weight, and prevent or even treat cancer. However, there’s little credible research showing the benefits of alkaline water.

Some studies also suggest that alkaline water might help slow bone loss, but further investigation is needed to determine if this influences overall bone mineral density and if the benefit is maintained over the long term.

The best rule of thumb is when you exercise, drink to thirst and hydrate your body with plain water and, as needed, a sports beverage.

— Katherine Zeratsky, R.D.N., Endocrinology/Nutrition, Mayo Clinic, Rochester, Minnesota