I drink around 3-3.5ltrs a day and make my shakes with 400-500ml of water so ups the intake as well.
It did take me a while to get used to drinking so much water. I did used to drink water, but with Robinsons R diluted juice, and around 3 pints a day! Used to think I was doing well.
A trick I did at the beginning was carry 500ml bottles around with me...for some reason you get through this so much more quickly. As soon as you get up, start sipping it....if you travel, sip it as well, and before you know it, you will be onto your first litre!
I now used 1.5ltr bottles as I dont find it so daunting seeing a bottle that size and knowing I need to drink two of them, and a little more besides.
I find that I need a bottle with me all the times as my mouth seems to get very dry..so keep it with you at all time, even when shopping.and just keep sipping,,,you will be surprised that it is easier than you think.
Break it down into hours, and minutes and then you will get an idea of how much you need to drink!
Keep at it though; the more the better!