Make guava lavender simple syrup: In a saucepan bring to a boil water, sugar, lavender, and sliced guavas. Reduced heat, stir and allow to simmer until all sugar is dissolved and guavas have become soft. Remove from heat, allow to cool, and strain. Push guavas with back to spoon to extract as much flavor as you can.

To a pitcher add half of the guava lavender syrup, lemon juice and water. Stir to combine, taste, and adjust for tartness. Add more syrup if too tart or add more lemon juice if too sweet. Serve over ice.