I watched an interesting programme on this the other day 2ltrs is the amount of water needed but the majority of this is in the foods we eat. Tea, Coffee and alcohol all count as the net amount is for hydration.

However, if you do want to up your amount have a small 500ml bottle on your desk and aim to drink 1 to mid morning, 1 to lunch, 1 to mid pm and then 1 before home. It's far less daunting than a big bottle