How much water?

Apologies if this has been posted before.

I know that we should drink a lot of water on SW, but how much is the right amount?
I generally don't drink plain water but drink it with sugar free squash or drink diet coke.
After my last week's disappointment with 1/2 pound gain, after sticking to plan 100%, I was advised that I should drink lots of plain water as it may help me.
As I really want to lose each week, no matter how little, I have decided to give it a bash.
I have drunk between four and five pints of water a day, at work, since. Is that enough or two much? I know it's giving me extra exercise as I am running up and down the stairs to the loo all day!

I've been aiming for 2.5lt a day and that is mainly squash & water as I can drink that easier than plain water.

I have always drunk a 2 litre bottle of water every day for year's as well as my other drinks, coffee etc, but since doing SW I have probably drunk about 3 litres, I buy 10 x 2 litre bottles of sparkling water a week so that is 20 litres per week, plus my hot drinks too - so I do drink quite a lot, but I like it, I don't like cola or any other 'pop' so I drink water instead.

Thanks ladies!
Good, so it looks as if it's not too much!
I count it in pints as I have a pint glass at work but 5 pints is about 2 litres and a bit.
That's just what I drink at work. In the evening I have about 3 or 4 pints of diet coke (again in pint glasses) with a tot of brandy in a couple!

I drink 2-3lts of water a day, not counting coffee and herbal teas. I only drink water plain if it's refrigerated or iced, or if it's room temperature I usually add these little sachets of 0 cal flavouring to it.