"Yelm", or home-made lemon squash. Updated 10 September 2021 and again 12 August 2022

It was my father, I think, who first called it "Yelm",  as a way of distinguishing it from other kinds of lemon drink.  Certainly my family have been making it for well over 50 years - I remember taking a supply to school in empty whisky bottles, which slightly disconcerted the House Mistress and Matron - it would have been a lot worse had I been bringing in whisky or gin in empty lemon squash bottles, of course.... Yelm, by the way, is very nice mixed with gin if you like gin.

Measurements are in Imperial, as that's what we used back in the day.  I'll put rough metric equivalents in brackets.

Rind and juice of 3 lemons
2 oz citric acid (approx 50g)
2 lbs sugar (a little less than 1 kg) (see note)

3 pints boiling water (1.75 litres)
Optionally, you could add elderflower blossoms or crushed mint (I love mint in lemon drinks so I used the latter).
Empty bottles - to take at least 2.25 litres

You can also use limes as well as, or instead of, lemons; if you use just limes, then use 4 as they are apt to be smaller.  Oranges work if mixed with lemons or limes, but render the finished drink too sweet on their own.   Today (September 2021) I am going to make lime and mint.

PLEASE NOTE: You really don't need 2 lbs of sugar - I'm now using 500g, and my mother just uses 1 lb.  So if you wish to cut down on sugar.... it's really "to taste".  Ordinary squash seems vilely sweet in comparison!

Mix everything together in a large jug or bowl and stir until the sugar and acid have dissolved.  Strain, and pour into bottles (if you don't strain, it doesn't last so long as the citrus peel is apt to go mouldy); keep in the fridge and dilute to taste.  I imagine that if you wanted lemon barley water, you could use this as a base instead of making from scratch......