As she said, why not buy the Cambridge water flavourings?
You can have 1 teaspoon per day, and this is supposed to be added to a litre of water, but with the summer berry flavouring I buy, I add it to 1.5 litres and it tastes just as nice (nicer I think!) as the flavouring is v strong. And 1.5 litres makes up quite a bit of my daily water so it really makes a difference.