Place the almonds in a food processor and blend to a smooth paste, adding a splash of water to loosen.
Place the measurement water and sugar in a heavy-based saucepan and bring to the boil, stirring continuously until the sugar has dissolved. Stir in the almond paste and simmer for 5 minutes. Stir in the orange blossom water and turn off the heat.
Leave to cool in the pan to let the flavours mingle, then pass through a muslin cloth into a jug and squeeze tightly to extract all the milky liquid from the almonds.
Pour into 4 glasses, add some ice cubes to each and serve immediately. Alternatively, chill the glasses in the refrigerator or freezer.