for a big bag of water
with a long tube sticking out of it
and a valve that you stick in your mouth and suck from like a straw
that you wear on your back
or on your hip
and use while cycling
, or other athletic activity
or actually anytime you want.
Camelbak started the craze around 10 years ago. Now there are multiple manufacturers, different designs (large backpacks, hip packs, aerodynamic packs, etc.) and a whole cottage industry of gadgets to clean, store, and dry out your hydration system.
If you're still cycling with a water bottle, you're drying out way too soon. I can finish 2 liters of water on a 1 hour bike ride--obviously I need it.