Combine raspberries and water in a flat-bottomed kettle; crush berries. Cover and bring to a boil. Reduce heat; simmer, uncovered, 10 minutes, stirring frequently. Strain berries through a dampened jelly bag, reserving 3 1/2 cups juice; discard pulp.
Combine reserved juice and lemon juice in kettle, stirring well; bring to a rolling boil. Add sugar, stirring until sugar dissolves. Continue to boil until mixture sheets from a cold metal spoon. Remove from heat, and skim off foam with a metal spoon.
Ladle jelly into hot sterilized jars, leaving 1/4- inch head space. Cover at once with metal lids; screw bands tight. Process jelly in boiling water bath 5 minutes.