Going for a workout? Great! Just be sure to protect against dehydration by drinking water before you start.

While there’s no “one size fits all” when it comes to how much someone should drink, a general rule is the hotter and more humid it is, the more you’ll sweat and the more fluid you’ll need, says Bob Murray, PhD, co-founder of the Gatorade Sports Science Institute in Barrington, Ill.

Still, sweat – or lack of – can be deceiving. Exercising in dry or cool climates produces little visible sweat due to evaporation, but the body is still losing moisture. And even mild exercise can be dehydrating.

Experts recommend drinking 4 to 8 oz. before, during and after a workout. The key is to drink before you’re thirsty, adds Murray, because thirst, along with fatigue, dry mouth, muscle cramps and dark, concentrated urine, are the first signs of dehydration. Knowing these signs can help you avoid the more serious consequences, such as dizziness, headache, nausea, diarrhea and heat exhaustion.

What you wear makes a difference, too. Light, loose-fitting, breathable fabrics will keep you cooler and minimize sweating.

Age, body weight and certain medications also influence hydration. Aging desensitizes the thirst mechanism, which means you’ll drink less; excess weight makes your body work harder and sweat more; and certain medications, including diuretics, antihistamines and blood pressure drugs, can cause fluid loss.

If chronic dehydration persists, it can increase the risks of some drugs’ side effects, such as kidney damage. Regardless of age or risk factors, drinking plenty of water throughout the day is a healthy habit.