Cut lemons into 1/8-inch-thick rounds; discard seeds. Stir together sugar, lemon juice, and water in a large skillet over medium heat until sugar is dissolved. Add lemon slices, and simmer gently, keeping slices in a single layer and turning occasionally, 14 to 16 minutes or until slightly translucent and rinds are softened. Remove from heat. Place slices in a single layer in a wax paper-lined jelly-roll pan, using tongs. Cool completely (about 1 hour). Cover and chill 2 hours to 2 days. Reserve syrup for another use.