Zest the lemons, being careful not to get any of the pith.
Place the zest in a bowl with 2x the amount of granulated sugar and mix well and muddle. Cover and let rest for 4 hours to make the oleo saccharum.
Bring twice as much water as the sugar to about 150 F.
Mix the water into the lemon sugar, then strain and squeeze well.
In a separate jar, squeeze the juice from the zested lemons.
Combine the syrup, juice, and some still or sparkling water into a glass in a 1:1:5 ratio, adjusting to taste.
