Crush the raspberries with the water.
Stretch gauze cloth between a stool, put quantity and drain the juice into a large enough bowl for several hours.
Or juice raspberries in elt. Juice raspberries in a juicer and filter through the gauze cloth. The yield is then higher.
Weigh out 400 g sugar per 1/2 l juice, bring to the boil very briefly while stirring, skim and bottle. If boiled too long, you get raspberry jelly.
Tip: In the same way, you can also cook currant syrup (red or possibly black), blackberry and cherry syrup (+pomegranate!).