I have just made a batch. My recipe was more or less the same as those mentioned.
4 Pints water
3/4 bag of sugar, about a pound and a half
2 lemons, 1 sliced, the rind of the other
About 25-30 flower heads
Boil the water and disolve the suger, leave to cool a bit. After about an hour pop in the flour heads and the lemon. Cover and leave for 24 hours.
Next day, bottle and pop in fridge!
No citric acid, just the juice of the lemon.
The mixture is lovely mixed with vodka. Or mixed with soda water / diet lemonade. Very refreshing taste of summer