Weigh the 900 grams of fruit - that will be approximately four oranges and half a grapefruit. Then halve them all including the lemon and squeeze the juice out, either by hand or with a power juicer.
Fill a large pan with the water and add the freshly extracted fruit juice. Now comes the laborious part, scraping out the pith from the fruit shells. it is important to get as much as possible as this is where the natural pectin is in the fruit and that is what makes the final preserve set to a nice thick jelly. Gather it all in a muslin bag, tie at the neck and suspend it in the liquid in the pan. This is to keep the solids out of the preserve while extracting as much fruit pectin as possible - along with some extra flavour too.
Now slice all the fruit shells into fine strips - you can decide how thick or thin, depending on your taste. Some people will dice them fairly small while others leave them in long, thick strips - its all a matter of personal taste.
Collect the sliced peel in a bowl and pour into the pan before setting it to simmer on a low heat for around 2 hours. You'll know when it is ready as the rind strips will be soft - if two hours isn't enough then give it around another 20-30 minutes max.
Now remove the rind bag, let it cool to touch and squeeze out as much juice as possible. Placing it between two plates and leaning on it with full weight is a great way to extract maximum juice. Then scrape off as much of the gelatinous goo as possible and pour it all back into the pan.
Now add the sugar to the mix, stirring until all crystals are dissolved before setting it to a rolling boil on a high heat for around 15 minutes - stirring occasionally to avoid burning.
Chill a plate in the fridge and pour a spoonful of the hot liquid onto it then return it to the fridge to cool right through. Now push it with your finger to see if it wrinkles - if it does it is ready, if not then keep the pan boiling for another 5-10 minutes until it is ready.
Place your clean jam jars in the oven to warm up - 5 minutes at 170c should do it.
Then cut out some greaseproof paper circles to fit inside the necks of your jars.
When the pan has cooled for around 15 minutes, ladel the liquid marmalade into the jars, place the greaseproof paper caps on then seal the lids. As the marmalade cools the lids will be pulled on tighter as the remaining air inside contracts.
And thats all there is to it. When its cooled completely the marmalade will be nicely jellified and taste scrumptious.