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You could add more lemon or lime to it too, that would be nice.
This is a recipe from River Cottage that includes orange, I might give that a go next year:
https://www.rivercottage.net/recipes/elderflower-cordial
Makes about 2 litres:
About 25 elderflower heads
Finely grated zest of 3 unwaxed lemons and 1 orange, plus their juice (about 150ml in total)
1.5 litres water
1kg sugar
1 heaped tsp citric acid (optional)

That sounds pretty good, too! So much goodness from the elder flowers! :D