Rinse unpeeled lemon and slice into very slender rounds, discarding the end pieces and any seeds. Place lemon slices in a small pan and stir in apricots and water. Bring mixture to a boil over high heat;reduceheat and simmer, uncovered, for 5 minutes. Remove mixture from heat and set aside.
Wash 5 half-pint jars. Keep hot until needed. Prepare lids as manufacturer directs.
Place pears in a heavy-bottomed 8- to 10-quart pan. Stir in sugar until well-blended. Bring mixture to a boil over medium heat, stirring occasionally.
Ladle the hot preserves into 1 hot jar at a time, leaving 1/4 inch head space. Wipe jar rim with a clean, damp cloth. Attach lid. Fill and close remaining jars. Process in a boiling-water canner for 10 minutes (15 minutes 1,000 to 6,000 feet; 20 minutes above 6,000 feet).