Add watermelon juice, white sugar and lemon juice to the pot. Give the mixture a stir and then add in the fruit pectin. Give it another stir and bring it to a full rolling boil while stirring frequently to prevent it from burning. The mixture should reach 220 degrees F. This takes about 20 minutes.

Once it reaches the desired temperature, carefully pour, ladle or funnel the liquid into half-pint jars. Wipe rims and secure the lids. Be careful, the jars are hot so use a kitchen towel when handling. Clean out your large pot or fill another one with hot water and cover the jars. Bring to a boil and allow the jars to hang out in the hot water bath for 10 minutes or so.

After 10 minutes, carefully remove the jars from the hot water and let them cool down. Make sure the seals are secure and store in a cool, dark place for up to one year.