Whether for school or work, you can always find a good use for a backpack. The material of choice for this bag is nylon and it has a one-litre volume.
From Amazon
Osprey Europe Duro 1.5 Unisex Running Hydration Pack with 2 x 250 ml Hydraulics Soft Flasks - Phoenix Red (M/L)
Trekkinn
Osprey Duro 1.5l Hydration Vest Red,White S-M
Sigma Sports
Osprey Duro 1.5 Hydration Pack - Red