Peel rind from lemons and grapefruit; cut into thin strips, about 1 in. long. Set aside fruit., In a Dutch oven, combine water and citrus peel. Bring to a boil. Reduce heat; cover and simmer 5 minutes or until peel is softened. Remove from heat and set aside., Trim white pith from reserved lemons and grapefruit; discard pith. Cut lemons and grapefruit into segments, discarding membranes and seeds. Chop pulp, reserving juices; stir into reserved peel mixture., Add pectin. Bring to a full rolling boil over high heat, stirring constantly. Stir in sugar; return to a full rolling boil. Boil and stir 1 minute., Remove from heat; skim off foam. Ladle hot mixture into six hot half-pint jars, leaving 1/4-in. headspace. Wipe rims. Center lids on jars; screw on bands until fingertip tight., Place jars into canner with simmering water, ensuring that they are completely covered with water. Bring to a boil; process for 10 minutes. Remove jars and cool.