Wash limes thoroughly, dry; using sharp knife, slice as finely as possible; retain any juice from limes; remove seeds (if there are any, as you slice).
Place sliced limes, any reserved juice and water in china, glass or plastic basin, cover, stand overnight.
Next day, pour lime mixture into large boiler, bring to boil, reduce heat, simmer covered for 30-45 mins or until rind is tender. It is important to cook fruit gently at this stage.
Remove lime mixture from heat; using measuring jug, measure mixture into large basin, return lime mixture to large boiler. Allow 1 cup sugar for each 1 cup of measured lime mixture.
Place sugar in large baking dish, place in slow oven for 10 minutes, stir several times. (Heated sugar will dissolve in the jam more quickly, resulting in clearer jam). Bring lime mixture to boil, add sugar all at once, (its better to add the sugar off the heat).
Stir until sugar is dissolved completely – do not allow to boil again until this happens; do not stir after marmalade boils. (It is important, once sugar is added that there is not too much mixture in the boiler; it should not be more than 5cm (2in) deep; this will allow maximum evaporation of liquid, resulting in a marmalade which will jell as quickly as possible.).
Bring marmalade to the boil, boil rapidly, uncovered. Place a saucer in the freezer for 10 minutes, before testing marmalade. After marmalade has been boiling rapidly for 12 minutes, remove from heat; allow bubbles to subside, drop a teaspoonful of marmalade on to a cold saucer, return to freezer for a few minutes to cool. If marmalade is not jelled enough, return to heat, cook further 3 minutes, test again in the same way. Marmalade should be jelled within 20 minutes; stand 5 minutes to allow fruit to settle. Pour into hot sterilized jars, Store in cool dark place.