In a 6- to 8-quart heavy pot combine half of the gooseberries and the water. Using a potato masher, crush berries slightly. Stir in the remaining gooseberries, sugar, mangoes, and lemon juice.
Bring mixture to boiling over medium heat, stirring constantly to dissolve sugar; reduce heat. Boil gently, uncovered, for 30 to 40 minutes or until mixture is thickened and sheets off a metal spoon, stirring frequently (jam will be a darker red in color). Remove from heat and quickly skim off foam with a metal spoon.
Ladle hot jam into hot sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.
Process filled jars in a boiling-water canner for 10 minutes (start timing when water returns to boiling). Remove jars from canner; cool on wire racks. Makes 6 half-pints.