Maybe your inner jogger needs a running backpack? If you prefer grey backpacks, then this should you just fine and it has a two-litre volume.
From Merlin Cycles
Camelbak Classic Light Hydration Pack - Gunmetal / 4 Litre
Certini
Camelbak Classic Light 4L Hydration Pack with 2L Reservoir - Gunmetal
This product is also available at 1 unverified store.