Hello and welcome.
I was told a minimum of 2L and a maximum of 6L. I tend to have about 3.5-4.5L a day but I don't include any coffee of have or water in my shakes in that. I do have a flapjack a day so I have to have a bit more coz of not having the water in the shake. I do make my shakes with 400-450ml water.
It is important that you space the water out throughout the day rather than try to drink too much too soon - that's when it can be bad for you!!!! I have a sports bottle with me at all times and sip from it (and others) regularly throughout the day.
You may find it easier to gradually build up the amount you drink. When I started LT I struggled to drink 2L a day, now I find I am thirsty for more!
Good luck.
x