Bring the water and berries to the boil, reduce the heat. Simmer until the berries burst, cover and leave to stand for approx. 10 mins. on the switched-off hob, pour through a jelly bag or sieve lined with a cheesecloth, drain. Don't squeeze out the berries otherwise the juice will become cloudy, pour the juice back into the pan.
Mix the sugar and lemon juice with the berry juice, bring to the boil while stirring, cook on a rolling boil for approx. 10 mins., stirring constantly. Skim off any foam. Ladle the jelly into the clean, pre-warmed jars while still boiling hot, fill the jars to just below the rim, seal immediately.