Players at this summer's World Cup will get three-minute cooling breaks and chilled benches to survive the heat. Fans? They've just been told they can't bring their own water bottles.

In a last-minute reversal now drawing backlash from fan groups, FIFA announced that spectators will no longer be allowed to carry empty, reusable, transparent bottles into stadiums — overturning an earlier decision that had cleared them across all 16 host cities in the U.S., Mexico and Canada. 

The timing is striking: This is a tournament where the heat is dangerous enough that organizers built a special heat policy around it.

(MORE: Heat can turn deadly fast)

And the numbers back that up. Weather.com senior meteorologist Jonathan Erdman did a deep dive on the temperatures players and fans could face, noting that stadiums in Miami and Monterrey, Mexico, face the most potential for extreme heat and humidity.

Miami’s average highs are around 90 degrees, but from mid-June through mid-July the average heat index is about 102 degrees.

Monterrey, Mexico, has seen mid-summer highs in the 110s.

Houston may face the most dangerous heat-humidity combo of any host city, you can read a lot more about that here.

Why the change?

The governing body says the reversal is due to safety concerns.

"FIFA is committed to protecting the health and safety of all players, referees, fans, volunteers, and staff," it told Reuters in a statement. "FIFA made the decision to prohibit bottles to prevent risk and injury to players and attendees."

An English fan group called the decision a “money-grab.”

In a statement the Free Lions group said, “For all of the effort they are going to with ‘drinks breaks’ for the players, this is such a strange, late change. We hope the water fountains in stadiums will still be free, hopefully you aren’t charged in the queue!”

The risk for fans

 "In a major sports tournament, there'll be lots of walking around the city for fans," said Theodore Keeping, a climate scientist at Imperial College London. 

He told Reuters, "There needs to be some way in which fans can get water that is not really expensive, because some people simply will make the choice not to buy water, and that puts fans at a high level of risk."

Dehydration and heat exhaustion can sneak up on you, doctors say once temperatures get above 90 degrees, your body’s ability to sweat and cool you off can stop functioning. Learn more about that here.

FIFA said measures would be in place to deal with the conditions.

"FIFA works closely with each Host City Committee and local authorities on heat mitigation factors for fans traveling to the stadium, which can include resources such as misting stations, fans, hydration stations, cooling tents and more around the stadium footprint," the statement said.