Hydration for Swimmers

Warding off dehydration while swimming at practice doesn’t need to be difficult. Start by showing up well-hydrated. Mullen suggests downing 16 ounces of water first thing in the morning. Keep a topped-off water bottle on the pool deck, and sip from it between sets. If you’re doing a long stretch of endurance training, swig from the bottle before your cooldown and make sure to rehydrate once you’re done.

https://www.triathlete.com/nutrition/race-fueling/yes-you-can-get-dehydrated-while-swimming/