It happens every year:

The racer thinks, "Hmm. Long ski race. A marathon. Need to stay hydrated. One water bottle isn't enough, and it's a pain to get at. My Camelbak works great for long bike rides. It'll be perfect for a 50 km race!"

Day of the race, the racer fills the Camelbak with water, puts it on, and heads out to test wax and warm up. Thirty minutes later, it's to the start line. We're off!

Time for the first feed, about 5 km into the race. Put the valve in the month and suck.

Nothing. 

"DAMN!"

The valve and hose are frozen solid. Not only does the racer not get a drink, that's over 4 pounds of extra weight that will have to be carried for the next 45 km...

Racing Rule #1

The first rule of racing: Never do anything you haven't tried first in training. Don't try new foods and certainly don't try a hydration system for the first time! The racer's first mistake was not testing the Camelbak  during some below freezing training sessions. That doesn't mean the Camelbak (or other hydration system) won't work during freezing temperatures, only that you need to test different options for keep your H2O liquid. 

Keeping Water from Freezing

Here's a few ideas to help keep you hydration system, whether it's a Camelbak or like system, or a plain old bike water bottle, from freezing. Let's start with bladder-based hydration systems:

	Start out with HOT water (not boiling) in your bladder. Cold water freezes faster (duh)...
	Keep the system warm - keep it in your car till the last moment, or wrap it in a jacket near the start. Use a water bottle before the race, and only put the hydration system on just before the start.
	The bite valve and hose will always freeze first. You need to keep them unfrozen. How? Try one or more of these different ways:
	Drink frequently so the wind-chilled water in the hose and valve is replaced by warmer water from the bladder. Blow air into the hose after every drink so that no water remains in the hose. Buy a Thermal Control Kit (Camelbak) or Drinking Tube (Platypus). These kits and the like provide an insulated drinking tub cover and/or valve cover.

I have successfully used my Camelbak Rocket during two-hour rollerski sessions at temperature in the high 20's, so I know they do work. I used hot water and drank frequently - every few minutes. I have not tried it at colder temperatures. 

How about water bottles?

	Start out with HOT water (not boiling) in your  bottle. Cold water freezes faster (duh)...
	Use one bottle during warm up, then replace it with a fresh bottle that been inside or otherwise insulated just before the race starts.
	To keep the nozzle from freezing, put your water bottle upside-down in your water bottle holster. Ice floats, so ice formation will float up to the bottom of the bottle, leaving the nozzle free of ice.
	Use an insulated water bottle. Polar makes one; I assume others make them, too. You still may want to wear the water bottle upside down...
	Ultimate used to make an insulated jacket for water bottles - I still have one from years ago. Check around, maybe some one else makes them now.

I've had frozen water bottle nozzles before (turn it upside down and shake - usually but not always, the water will melt the ice), but never when I've put the bottle upside down in my holster. And I always use hot water in cold temperatures.

Of course, there are other options. If it's a short race. don't take water. If there are feed stations, get water there - just make sure you verify there actually are feed stations and that they actually have water!

Plan ahead. Test during training. Stay hydrated.