A clear decoction of pearl barley, sweetened with sugar and brightened with lemon juice, drunk warm or cool. The most common domestic remedy of learned England.

Why this dish? Locke often followed his own medical prescriptions and distrusted excess. Barley water, warm and refreshing, is precisely the kind of mild drink that an asthmatic physician-philosopher prepared to soothe the chest and temper the humours.

When my chest oppresses me, or fever threatens, I resort to this simple remedy rather than the violent drugs of apothecaries. One boils barley in plenty of water, strains it through cloth, and renders this water pleasant with a little sugar and the juice of a lemon, a fruit that ships bring us from the South. Drink it warm, in small sips throughout the day: it soothes the inner acrimonies and quenches thirst without burdening the stomach. Trust the experience of a man who has been his own physician.

How it was made : Barley water is a long-attested domestic remedy in England, recommended for fevers, chest ailments and irritated stomachs. It was flavoured with lemon, orange peel or liquorice. 17th-century physicians, heirs to humoral theory, prescribed it as a 'cooling' drink in the Galenic sense.

The contemporary twist : Serve it over ice in a glass, with a ribbon of lemon zest and a sprig of mint: the oldest of 'detox waters', four centuries old and still going strong.

John Locke · Charactorium