The hydration system is very important for racers in RacingThePlanet Ultramarathons. You must carry containers that can hold 2.5 liters of water at all times. The main choices are: 1. Bottles: These allow for more flexibility – they can be attached to the shoulder straps of your backpack, put in a front pack, kept in the side of the backpack or carried by hand. 2. Hydration bladders: A popular choice, but sometimes difficult to know how much fluid you have remaining and are prone to leak and can be difficult to fill quickly. 3. Soft bottle: Platypus or Salomon, at least 1 liter in capacity. The most popular hydration system is a water bottle with a straw attached to the front of the backpack with a soft bottle as backup.