Warm up a ltr of the water and dissolve the sugar in it. Pour it and the rest of the water into a large, plastic or wooden container/bucket.
Grate or peel the lemon skin and add the zest to the bucket along with the juice of the lemons and the white wine vinegar. Give the contents another good stir.
Add the elderflower heads (which have their own yeast), making sure you put them in with their heads facing downwards and stems 'poking' out of the water. Alternatively, you could take a fork and use it to take the flowers off, leaving the stalks behind. If you can't find large flower heads, then add another 5 -10 flower heads. Give the contents a gentle stir and cover with a clean tea towel. Leave in a warm, dark cupboard for 2 - 5 days, until fermentation has completed. After 2 days check you're champagne, which, at this stage, should be showing a mold on the liquid, around the flower heads.
Once fermentation is complete, gather another bucket, some air tight bottles, a sieve, jug and some muslin cloth. Make sure you sterilise the aforementioned equipment. Scoop out everything floating on top of the liquid in your container. Fold your muslin into four and place it over the sieve. (I use my husband's old shirts!) and using the jug, sieve the liquid contents into the empty, sterilised bucket/container, leaving about 2 inches of liquid behind. (this allows for any sediment to be left behind) Leave for about an hour, to allow any further sediment to settle.
Once you've completed the above step, it's time to bottle the champagne. Using your jug, a funnel and muslin cloth, decant the contents of the bucket into the bottles. Remember to leave another couple of inches behind to allow for any sediment. Place your bottles in a dry, warm cupboard for approx 2 weeks, and hey presto...party time. And don't forget my invite. ;)