Squeeze lemons and set juice aside.
Place lemon skins into a large pot and cover with water. Bring to boil and simmer for 30-40 minutes until the skins are soft. Cool completely. Squeeze skins and scrape out the remaining lemon from the skins. Discard skins.
Add sugar and bring to the boil until sugar is dissolved.
Add reserved juice and citric acid and stir to combine.
Dilute to taste and serve over ice.
Keep remaining syrup in the fridge until use.
This makes a lot!