I've not used a hydration pack for cycling (yet) but when I've gotten home from hiking I will fill it halfway with fresh water and add baking soda. Freeze overnight and then thaw and drain upside down for several hours. No problems reusing.
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Everyone thinks they have had a long strange trip, until they look at other folks' journeys. Then they realize everyone has had a long strange trip, just using different modes of transportation.
"The mystery of life isn't a problem to solve, but a reality to experience."