I would also add that it is better to gradually up your water intake rather than try to start on 3-4L. When I started LT I was hard pushed to get 2L down me now I'm thirsty if I have less than 3L!!! Build it up gradually, say 200ml extra each day or so and you'll be up to another litre in a week!
I make the task less daunting by drinking out of 500ml/750ml bottles. I have a 750ml in the car to sip at to and from work, 2 500ml bottles in my bag at work which I can refill as needed and another 750ml for the evening. If I'm out shopping I always have a 500ml bottle in my handbag. I always have a bottle by the bed to sip from during the night if I need it. You'd be amazed at how quickly you get through them after a while - I drank over a litre this evening in the 2hours my youngest was at a swimming gala and I did it without thinking!
Good luck.
x