Wash the zucchini, peel and halve lengthways, remove the seeds and coarsely grate the pulp. Peel and dice the apples. Cover the apples and zucchini with the water in a saucepan and bring to the boil for 8 to 10 minutes over low heat. Add the preserving sugar, bring to the boil and let it simmer for about 3 minutes. Make a gel test! Pour into jars rinsed with hot water and close.