Bring water to a boil in a large saucepan, stir in lavender flowers, remove from heat and let steep for about 20 minutes. After steeping, strain liquid into a separate bowl and discard the lavender flowers. Stir in lemon juice and pectin until the pectin is completely dissolved.
Place mixture back into saucepan and bring to a boil over high heat; add sugar. Continue to allow mixture to boil at a hard rolling boil for 2 to 4 minutes, stirring occasionally.
After boiling, transfer the jelly into hot sterilized jars. Fill them to within 1/4 inch of the top, wipe any spilled jam off the top, seal the lid and tighten the ring around them.