SPRINGFIELD, Ill (WAND) - To make sure a person is staying hydrated, people refer to the "8x8 rule" - drinking eight 8-ounce glasses of water a day.

Health experts have said it is generically true, but it depends on the person. 

The National Weather Service said the weather in central Illinois is expected to be hotter than usual. The heat index would feel like it is up to 115 degrees. Statistics shows how heat causes more fatalities than any other weather hazard. 

Dr. Shaugn Reid said it is important to stay hydrated. 

"They say your body is made up of 60 percent water, so you want to be consuming a lot of it," Reid said. 

When it comes to the "8x8" rule, Reid usually tells his patients to drink "half the body weight in ounces".

"Anything beyond a gallon is probably unnecessary," Dr. Reid added. 

The rule may not be meant for a specific individual. A person's water intake depends on what they've been doing throughout the day. Â