Known in England by this name at least since 1663 (OED) lemonade is traditionally sweetened lemon-juice and water, but in England the drink is now almost universally a distinctive sparkling water flavoured with sugar, sweeteners and acids to imitate lemon. The product sold as 'lemonade' frequently contains very little or no lemon.

Lemons were clearly once very expensive in England, so the practice of making fake lemonade is not by any means new. A receipt from the 18th Century uses 'oil of sulphur', what we now call Sulphuric Acid, while more recent versions use citric or tartaric acid.

Original Receipt from 'Secrets Concerning Arts and Trades', published in 1795

XIV. Lemonade water at a cheap rate.
Dissolve half 2 pound of sugar in a quart of water; rasp over it the yellow part of one, two, or three lemons, as you, like, and mix a few drops of essential oil of sulfur in the liquor. Then cut three or four slices of lemon in the bowl, when you put the liquor in it.


Original Receipt from 'Pot-luck; or, The British home cookery book' by May Byron (Byron 1914)

987. LEMONADE (Sussex)
Two pounds of castor sugar, one ounce of citric acid, the grated rind of three oranges, three tumblerfuls of cold water. Let it stand three or four days, stirring occasionally. Then strain, bottle, and cork tight.

988. LEMONADE SYRUP (Lancashire)
Take two ounces of citric acid, two scruples of essence of lemon; rub these thoroughly together


Original Receipt in 'The Art of Cookery Made Easy and Refined' By John Mollard (Mollard 1802)

LEMONADE OR ORANGEADE.
To a gallon of spring water add some cinnamon and cloves, plenty of orange and lemon juices, with a bit of each peel; sweeten well with loaf sugar, and whisk with it the whites of six eggs and one yolk. Put it over a brisk fire, and when it boils let it simmer ten minutes; then run it through a jelly bag, and let it stand till cold before it is drunk. This mode is recommended, the liquor having been boiled.